lib/less/parser/parser.js
function Parser(context, imports, fileInfo) {
    var parsers,
        parserInput = getParserInput();

    function error(msg, type) {
        throw new LessError(
            {
                index: parserInput.i,
                filename: fileInfo.filename,
                type: type || 'Syntax',
                message: msg
            },
            imports
        );
    }

    function expect(arg, msg) {
        // some older browsers return typeof 'function' for RegExp
        var result = (arg instanceof Function) ? arg.call(parsers) : parserInput.$re(arg);
        if (result) {
            return result;
        }
        
        error(msg || (typeof arg === 'string'
            ? 'expected \'' + arg + '\' got \'' + parserInput.currentChar() + '\''
            : 'unexpected token'));
    }

    // Specialization of expect()
    function expectChar(arg, msg) {
        if (parserInput.$char(arg)) {
            return arg;
        }
        error(msg || 'expected \'' + arg + '\' got \'' + parserInput.currentChar() + '\'');
    }

    function getDebugInfo(index) {
        var filename = fileInfo.filename;

        return {
            lineNumber: utils.getLocation(index, parserInput.getInput()).line + 1,
            fileName: filename
        };
    }

    /**
     *  Used after initial parsing to create nodes on the fly
     * 
     *  @param {String} str          - string to parse 
     *  @param {Array}  parseList    - array of parsers to run input through e.g. ["value", "important"]
     *  @param {Number} currentIndex - start number to begin indexing
     *  @param {Object} fileInfo     - fileInfo to attach to created nodes
     */
    function parseNode(str, parseList, currentIndex, fileInfo, callback) {
        var result, returnNodes = [];
        var parser = parserInput;

        try {
            parser.start(str, false, function fail(msg, index) {
                callback({
                    message: msg,
                    index: index + currentIndex
                });
            });
            for (var x = 0, p, i; (p = parseList[x]); x++) {
                i = parser.i;
                result = parsers[p]();
                if (result) {
                    result._index = i + currentIndex;
                    result._fileInfo = fileInfo;
                    returnNodes.push(result);
                }
                else {
                    returnNodes.push(null);
                }
            }

            var endInfo = parser.end();
            if (endInfo.isFinished) {
                callback(null, returnNodes);
            }
            else {
                callback(true, null);
            }
        } catch (e) {
            throw new LessError({
                index: e.index + currentIndex,
                message: e.message
            }, imports, fileInfo.filename);
        }
    }
    
    //
    // The Parser
    //
    return {
        parserInput: parserInput,
        imports: imports,
        fileInfo: fileInfo,
        parseNode: parseNode,
        //
        // Parse an input string into an abstract syntax tree,
        // @param str A string containing 'less' markup
        // @param callback call `callback` when done.
        // @param [additionalData] An optional map which can contains vars - a map (key, value) of variables to apply
        //
        parse: function (str, callback, additionalData) {
            var root, error = null, globalVars, modifyVars, ignored, preText = '';

            globalVars = (additionalData && additionalData.globalVars) ? Parser.serializeVars(additionalData.globalVars) + '\n' : '';
            modifyVars = (additionalData && additionalData.modifyVars) ? '\n' + Parser.serializeVars(additionalData.modifyVars) : '';

            if (context.pluginManager) {
                var preProcessors = context.pluginManager.getPreProcessors();
                for (var i = 0; i < preProcessors.length; i++) {
                    str = preProcessors[i].process(str, { context: context, imports: imports, fileInfo: fileInfo });
                }
            }

            if (globalVars || (additionalData && additionalData.banner)) {
                preText = ((additionalData && additionalData.banner) ? additionalData.banner : '') + globalVars;
                ignored = imports.contentsIgnoredChars;
                ignored[fileInfo.filename] = ignored[fileInfo.filename] || 0;
                ignored[fileInfo.filename] += preText.length;
            }

            str = str.replace(/\r\n?/g, '\n');
            // Remove potential UTF Byte Order Mark
            str = preText + str.replace(/^\uFEFF/, '') + modifyVars;
            imports.contents[fileInfo.filename] = str;

            // Start with the primary rule.
            // The whole syntax tree is held under a Ruleset node,
            // with the `root` property set to true, so no `{}` are
            // output. The callback is called when the input is parsed.
            try {
                parserInput.start(str, context.chunkInput, function fail(msg, index) {
                    throw new LessError({
                        index: index,
                        type: 'Parse',
                        message: msg,
                        filename: fileInfo.filename
                    }, imports);
                });

                tree.Node.prototype.parse = this;
                root = new tree.Ruleset(null, this.parsers.primary());
                tree.Node.prototype.rootNode = root;
                root.root = true;
                root.firstRoot = true;
                root.functionRegistry = functionRegistry.inherit();
                
            } catch (e) {
                return callback(new LessError(e, imports, fileInfo.filename));
            }

            // If `i` is smaller than the `input.length - 1`,
            // it means the parser wasn't able to parse the whole
            // string, so we've got a parsing error.
            //
            // We try to extract a \n delimited string,
            // showing the line where the parse error occurred.
            // We split it up into two parts (the part which parsed,
            // and the part which didn't), so we can color them differently.
            var endInfo = parserInput.end();
            if (!endInfo.isFinished) {

                var message = endInfo.furthestPossibleErrorMessage;

                if (!message) {
                    message = 'Unrecognised input';
                    if (endInfo.furthestChar === '}') {
                        message += '. Possibly missing opening \'{\'';
                    } else if (endInfo.furthestChar === ')') {
                        message += '. Possibly missing opening \'(\'';
                    } else if (endInfo.furthestReachedEnd) {
                        message += '. Possibly missing something';
                    }
                }

                error = new LessError({
                    type: 'Parse',
                    message: message,
                    index: endInfo.furthest,
                    filename: fileInfo.filename
                }, imports);
            }

            var finish = function (e) {
                e = error || e || imports.error;

                if (e) {
                    if (!(e instanceof LessError)) {
                        e = new LessError(e, imports, fileInfo.filename);
                    }

                    return callback(e);
                }
                else {
                    return callback(null, root);
                }
            };

            if (context.processImports !== false) {
                new visitors.ImportVisitor(imports, finish)
                    .run(root);
            } else {
                return finish();
            }
        },

        //
        // Here in, the parsing rules/functions
        //
        // The basic structure of the syntax tree generated is as follows:
        //
        //   Ruleset ->  Declaration -> Value -> Expression -> Entity
        //
        // Here's some Less code:
        //
        //    .class {
        //      color: #fff;
        //      border: 1px solid #000;
        //      width: @w + 4px;
        //      > .child {...}
        //    }
        //
        // And here's what the parse tree might look like:
        //
        //     Ruleset (Selector '.class', [
        //         Declaration ("color",  Value ([Expression [Color #fff]]))
        //         Declaration ("border", Value ([Expression [Dimension 1px][Keyword "solid"][Color #000]]))
        //         Declaration ("width",  Value ([Expression [Operation " + " [Variable "@w"][Dimension 4px]]]))
        //         Ruleset (Selector [Element '>', '.child'], [...])
        //     ])
        //
        //  In general, most rules will try to parse a token with the `$re()` function, and if the return
        //  value is truly, will return a new node, of the relevant type. Sometimes, we need to check
        //  first, before parsing, that's when we use `peek()`.
        //
        parsers: parsers = {
            //
            // The `primary` rule is the *entry* and *exit* point of the parser.
            // The rules here can appear at any level of the parse tree.
            //
            // The recursive nature of the grammar is an interplay between the `block`
            // rule, which represents `{ ... }`, the `ruleset` rule, and this `primary` rule,
            // as represented by this simplified grammar:
            //
            //     primary  →  (ruleset | declaration)+
            //     ruleset  →  selector+ block
            //     block    →  '{' primary '}'
            //
            // Only at one point is the primary rule not called from the
            // block rule: at the root level.
            //
            primary: function () {
                var mixin = this.mixin, root = [], node;

                while (true) {
                    while (true) {
                        node = this.comment();
                        if (!node) { break; }
                        root.push(node);
                    }
                    // always process comments before deciding if finished
                    if (parserInput.finished) {
                        break;
                    }
                    if (parserInput.peek('}')) {
                        break;
                    }

                    node = this.extendRule();
                    if (node) {
                        root = root.concat(node);
                        continue;
                    }

                    node = mixin.definition() || this.declaration() || this.ruleset() ||
                        mixin.call(false, false) || this.variableCall() || this.entities.call() || this.atrule();
                    if (node) {
                        root.push(node);
                    } else {
                        var foundSemiColon = false;
                        while (parserInput.$char(';')) {
                            foundSemiColon = true;
                        }
                        if (!foundSemiColon) {
                            break;
                        }
                    }
                }

                return root;
            },

            // comments are collected by the main parsing mechanism and then assigned to nodes
            // where the current structure allows it
            comment: function () {
                if (parserInput.commentStore.length) {
                    var comment = parserInput.commentStore.shift();
                    return new(tree.Comment)(comment.text, comment.isLineComment, comment.index, fileInfo);
                }
            },

            //
            // Entities are tokens which can be found inside an Expression
            //
            entities: {
                mixinLookup: function() {
                    return parsers.mixin.call(true, true);
                },
                //
                // A string, which supports escaping " and '
                //
                //     "milky way" 'he\'s the one!'
                //
                quoted: function (forceEscaped) {
                    var str, index = parserInput.i, isEscaped = false;

                    parserInput.save();
                    if (parserInput.$char('~')) {
                        isEscaped = true;
                    } else if (forceEscaped) {
                        parserInput.restore();
                        return;
                    }

                    str = parserInput.$quoted();
                    if (!str) {
                        parserInput.restore();
                        return;
                    }
                    parserInput.forget();

                    return new(tree.Quoted)(str.charAt(0), str.substr(1, str.length - 2), isEscaped, index, fileInfo);
                },

                //
                // A catch-all word, such as:
                //
                //     black border-collapse
                //
                keyword: function () {
                    var k = parserInput.$char('%') || parserInput.$re(/^\[?(?:[\w-]|\\(?:[A-Fa-f0-9]{1,6} ?|[^A-Fa-f0-9]))+\]?/);
                    if (k) {
                        return tree.Color.fromKeyword(k) || new(tree.Keyword)(k);
                    }
                },

                //
                // A function call
                //
                //     rgb(255, 0, 255)
                //
                // The arguments are parsed with the `entities.arguments` parser.
                //
                call: function () {
                    var name, args, func, index = parserInput.i;

                    // http://jsperf.com/case-insensitive-regex-vs-strtolower-then-regex/18
                    if (parserInput.peek(/^url\(/i)) {
                        return;
                    }

                    parserInput.save();

                    name = parserInput.$re(/^([\w-]+|%|progid:[\w\.]+)\(/);
                    if (!name) {
                        parserInput.forget(); 
                        return;
                    }

                    name = name[1];
                    func = this.customFuncCall(name);
                    if (func) {
                        args = func.parse();
                        if (args && func.stop) {
                            parserInput.forget();
                            return args;
                        }
                    }

                    args = this.arguments(args);

                    if (!parserInput.$char(')')) {
                        parserInput.restore('Could not parse call arguments or missing \')\'');
                        return;
                    }

                    parserInput.forget();
                    
                    return new(tree.Call)(name, args, index, fileInfo);
                },
                
                //
                // Parsing rules for functions with non-standard args, e.g.:
                //
                //     boolean(not(2 > 1))
                //
                //     This is a quick prototype, to be modified/improved when
                //     more custom-parsed funcs come (e.g. `selector(...)`)
                //

                customFuncCall: function (name) {
                    /* Ideally the table is to be moved out of here for faster perf.,
                       but it's quite tricky since it relies on all these `parsers`
                       and `expect` available only here */
                    return {
                        alpha:   f(parsers.ieAlpha, true),
                        boolean: f(condition),
                        'if':    f(condition)
                    }[name.toLowerCase()];

                    function f(parse, stop) {
                        return {
                            parse: parse, // parsing function
                            stop:  stop   // when true - stop after parse() and return its result, 
                                          // otherwise continue for plain args
                        };
                    }
                
                    function condition() {
                        return [expect(parsers.condition, 'expected condition')];
                    }
                },

                arguments: function (prevArgs) {
                    var argsComma = prevArgs || [],
                        argsSemiColon = [],
                        isSemiColonSeparated, value;

                    parserInput.save();

                    while (true) {
                        if (prevArgs) {
                            prevArgs = false;
                        } else {
                            value = parsers.detachedRuleset() || this.assignment() || parsers.expression();
                            if (!value) {
                                break;
                            }

                            if (value.value && value.value.length == 1) {
                                value = value.value[0];
                            }

                            argsComma.push(value);
                        }

                        if (parserInput.$char(',')) {
                            continue;
                        }

                        if (parserInput.$char(';') || isSemiColonSeparated) {
                            isSemiColonSeparated = true;
                            value = (argsComma.length < 1) ? argsComma[0]
                                : new tree.Value(argsComma);
                            argsSemiColon.push(value);
                            argsComma = [];
                        }
                    }

                    parserInput.forget();
                    return isSemiColonSeparated ? argsSemiColon : argsComma;
                },
                literal: function () {
                    return this.dimension() ||
                           this.color() ||
                           this.quoted() ||
                           this.unicodeDescriptor();
                },

                // Assignments are argument entities for calls.
                // They are present in ie filter properties as shown below.
                //
                //     filter: progid:DXImageTransform.Microsoft.Alpha( *opacity=50* )
                //

                assignment: function () {
                    var key, value;
                    parserInput.save();
                    key = parserInput.$re(/^\w+(?=\s?=)/i);
                    if (!key) {
                        parserInput.restore();
                        return;
                    }
                    if (!parserInput.$char('=')) {
                        parserInput.restore();
                        return;
                    }
                    value = parsers.entity();
                    if (value) {
                        parserInput.forget();
                        return new(tree.Assignment)(key, value);
                    } else {
                        parserInput.restore();
                    }
                },

                //
                // Parse url() tokens
                //
                // We use a specific rule for urls, because they don't really behave like
                // standard function calls. The difference is that the argument doesn't have
                // to be enclosed within a string, so it can't be parsed as an Expression.
                //
                url: function () {
                    var value, index = parserInput.i;

                    parserInput.autoCommentAbsorb = false;

                    if (!parserInput.$str('url(')) {
                        parserInput.autoCommentAbsorb = true;
                        return;
                    }

                    value = this.quoted() || this.variable() || this.property() ||
                            parserInput.$re(/^(?:(?:\\[\(\)'"])|[^\(\)'"])+/) || '';

                    parserInput.autoCommentAbsorb = true;

                    expectChar(')');

                    return new(tree.URL)((value.value != null || 
                        value instanceof tree.Variable || 
                        value instanceof tree.Property) ?
                        value : new(tree.Anonymous)(value, index), index, fileInfo);
                },

                //
                // A Variable entity, such as `@fink`, in
                //
                //     width: @fink + 2px
                //
                // We use a different parser for variable definitions,
                // see `parsers.variable`.
                //
                variable: function () {
                    var ch, name, index = parserInput.i;

                    parserInput.save();
                    if (parserInput.currentChar() === '@' && (name = parserInput.$re(/^@@?[\w-]+/))) {
                        ch = parserInput.currentChar();
                        if (ch === '(' || ch === '[' && !parserInput.prevChar().match(/^\s/)) {
                            // this may be a VariableCall lookup
                            var result = parsers.variableCall(name);
                            if (result) {
                                parserInput.forget();
                                return result;
                            }
                        }
                        parserInput.forget();
                        return new(tree.Variable)(name, index, fileInfo);
                    }
                    parserInput.restore();
                },

                // A variable entity using the protective {} e.g. @{var}
                variableCurly: function () {
                    var curly, index = parserInput.i;

                    if (parserInput.currentChar() === '@' && (curly = parserInput.$re(/^@\{([\w-]+)\}/))) {
                        return new(tree.Variable)('@' + curly[1], index, fileInfo);
                    }
                },
                //
                // A Property accessor, such as `$color`, in
                //
                //     background-color: $color
                //
                property: function () {
                    var name, index = parserInput.i;

                    if (parserInput.currentChar() === '$' && (name = parserInput.$re(/^\$[\w-]+/))) {
                        return new(tree.Property)(name, index, fileInfo);
                    }
                },

                // A property entity useing the protective {} e.g. ${prop}
                propertyCurly: function () {
                    var curly, index = parserInput.i;

                    if (parserInput.currentChar() === '$' && (curly = parserInput.$re(/^\$\{([\w-]+)\}/))) {
                        return new(tree.Property)('$' + curly[1], index, fileInfo);
                    }
                },
                //
                // A Hexadecimal color
                //
                //     #4F3C2F
                //
                // `rgb` and `hsl` colors are parsed through the `entities.call` parser.
                //
                color: function () {
                    var rgb;

                    if (parserInput.currentChar() === '#' && (rgb = parserInput.$re(/^#([A-Fa-f0-9]{8}|[A-Fa-f0-9]{6}|[A-Fa-f0-9]{3,4})/))) {
                        return new(tree.Color)(rgb[1], undefined, rgb[0]);
                    }
                },

                colorKeyword: function () {
                    parserInput.save();
                    var autoCommentAbsorb = parserInput.autoCommentAbsorb;
                    parserInput.autoCommentAbsorb = false;
                    var k = parserInput.$re(/^[_A-Za-z-][_A-Za-z0-9-]+/);
                    parserInput.autoCommentAbsorb = autoCommentAbsorb;
                    if (!k) {
                        parserInput.forget();
                        return;
                    }
                    parserInput.restore();
                    var color = tree.Color.fromKeyword(k);
                    if (color) {
                        parserInput.$str(k);
                        return color;
                    }
                },

                //
                // A Dimension, that is, a number and a unit
                //
                //     0.5em 95%
                //
                dimension: function () {
                    if (parserInput.peekNotNumeric()) {
                        return;
                    }

                    var value = parserInput.$re(/^([+-]?\d*\.?\d+)(%|[a-z_]+)?/i);
                    if (value) {
                        return new(tree.Dimension)(value[1], value[2]);
                    }
                },

                //
                // A unicode descriptor, as is used in unicode-range
                //
                // U+0??  or U+00A1-00A9
                //
                unicodeDescriptor: function () {
                    var ud;

                    ud = parserInput.$re(/^U\+[0-9a-fA-F?]+(\-[0-9a-fA-F?]+)?/);
                    if (ud) {
                        return new(tree.UnicodeDescriptor)(ud[0]);
                    }
                },

                //
                // JavaScript code to be evaluated
                //
                //     `window.location.href`
                //
                javascript: function () {
                    var js, index = parserInput.i;

                    parserInput.save();

                    var escape = parserInput.$char('~');
                    var jsQuote = parserInput.$char('`');

                    if (!jsQuote) {
                        parserInput.restore();
                        return;
                    }

                    js = parserInput.$re(/^[^`]*`/);
                    if (js) {
                        parserInput.forget();
                        return new(tree.JavaScript)(js.substr(0, js.length - 1), Boolean(escape), index, fileInfo);
                    }
                    parserInput.restore('invalid javascript definition');
                }
            },

            //
            // The variable part of a variable definition. Used in the `rule` parser
            //
            //     @fink:
            //
            variable: function () {
                var name;

                if (parserInput.currentChar() === '@' && (name = parserInput.$re(/^(@[\w-]+)\s*:/))) { return name[1]; }
            },

            //
            // Call a variable value to retrieve a detached ruleset
            // or a value from a detached ruleset's rules.
            //
            //     @fink();
            //     @fink;
            //     color: @fink[@color];
            //
            variableCall: function (parsedName) {
                var lookups, important, i = parserInput.i,
                    inValue = !!parsedName, name = parsedName;

                parserInput.save();

                if (name || (parserInput.currentChar() === '@'
                    && (name = parserInput.$re(/^(@[\w-]+)(\(\s*\))?/)))) {

                    lookups = this.mixin.ruleLookups();

                    if (!lookups && ((inValue && parserInput.$str('()') !== '()') || (name[2] !== '()'))) {
                        parserInput.restore('Missing \'[...]\' lookup in variable call');
                        return;
                    }

                    if (!inValue) {
                        name = name[1];
                    }

                    if (lookups && parsers.important()) {
                        important = true;
                    }

                    var call = new tree.VariableCall(name, i, fileInfo);
                    if (!inValue && parsers.end()) {
                        parserInput.forget();
                        return call;
                    }
                    else {
                        parserInput.forget();
                        return new tree.NamespaceValue(call, lookups, important, i, fileInfo);
                    }
                }

                parserInput.restore();
            },

            //
            // extend syntax - used to extend selectors
            //
            extend: function(isRule) {
                var elements, e, index = parserInput.i, option, extendList, extend;

                if (!parserInput.$str(isRule ? '&:extend(' : ':extend(')) {
                    return;
                }

                do {
                    option = null;
                    elements = null;
                    while (!(option = parserInput.$re(/^(all)(?=\s*(\)|,))/))) {
                        e = this.element();
                        if (!e) {
                            break;
                        }
                        if (elements) {
                            elements.push(e);
                        } else {
                            elements = [ e ];
                        }
                    }

                    option = option && option[1];
                    if (!elements) {
                        error('Missing target selector for :extend().');
                    }
                    extend = new(tree.Extend)(new(tree.Selector)(elements), option, index, fileInfo);
                    if (extendList) {
                        extendList.push(extend);
                    } else {
                        extendList = [ extend ];
                    }
                } while (parserInput.$char(','));

                expect(/^\)/);

                if (isRule) {
                    expect(/^;/);
                }

                return extendList;
            },

            //
            // extendRule - used in a rule to extend all the parent selectors
            //
            extendRule: function() {
                return this.extend(true);
            },

            //
            // Mixins
            //
            mixin: {
                //
                // A Mixin call, with an optional argument list
                //
                //     #mixins > .square(#fff);
                //     #mixins.square(#fff);
                //     .rounded(4px, black);
                //     .button;
                //
                // We can lookup / return a value using the lookup syntax:
                //
                //     color: #mixin.square(#fff)[@color];
                //
                // The `while` loop is there because mixins can be
                // namespaced, but we only support the child and descendant
                // selector for now.
                //
                call: function (inValue, getLookup) {
                    var s = parserInput.currentChar(), important = false, lookups,
                        index = parserInput.i, elements, args, hasParens;

                    if (s !== '.' && s !== '#') { return; }

                    parserInput.save(); // stop us absorbing part of an invalid selector

                    elements = this.elements();

                    if (elements) {
                        if (parserInput.$char('(')) {
                            args = this.args(true).args;
                            expectChar(')');
                            hasParens = true;
                        }

                        if (getLookup !== false) {
                            lookups = this.ruleLookups();
                        }
                        if (getLookup === true && !lookups) {
                            parserInput.restore();
                            return;
                        }

                        if (inValue && !lookups && !hasParens) {
                            // This isn't a valid in-value mixin call
                            parserInput.restore();
                            return;
                        }

                        if (!inValue && parsers.important()) {
                            important = true;
                        }

                        if (inValue || parsers.end()) {
                            parserInput.forget();
                            var mixin = new(tree.mixin.Call)(elements, args, index, fileInfo, !lookups && important);
                            if (lookups) {
                                return new tree.NamespaceValue(mixin, lookups, important);
                            }
                            else {
                                return mixin;
                            }
                        }
                    }

                    parserInput.restore();
                },
                /**
                 * Matching elements for mixins
                 * (Start with . or # and can have > )
                 */
                elements: function() {
                    var elements, e, c, elem, elemIndex,
                        re = /^[#.](?:[\w-]|\\(?:[A-Fa-f0-9]{1,6} ?|[^A-Fa-f0-9]))+/;
                    while (true) {
                        elemIndex = parserInput.i;
                        e = parserInput.$re(re);
                        
                        if (!e) {
                            break;
                        }
                        elem = new(tree.Element)(c, e, false, elemIndex, fileInfo);
                        if (elements) {
                            elements.push(elem);
                        } else {
                            elements = [ elem ];
                        }
                        c = parserInput.$char('>');
                    }
                    return elements;
                },
                args: function (isCall) {
                    var entities = parsers.entities,
                        returner = { args:null, variadic: false },
                        expressions = [], argsSemiColon = [], argsComma = [],
                        isSemiColonSeparated, expressionContainsNamed, name, nameLoop,
                        value, arg, expand, hasSep = true; 

                    parserInput.save();

                    while (true) {
                        if (isCall) {
                            arg = parsers.detachedRuleset() || parsers.expression();
                        } else {
                            parserInput.commentStore.length = 0;
                            if (parserInput.$str('...')) {
                                returner.variadic = true;
                                if (parserInput.$char(';') && !isSemiColonSeparated) {
                                    isSemiColonSeparated = true;
                                }
                                (isSemiColonSeparated ? argsSemiColon : argsComma)
                                    .push({ variadic: true });
                                break;
                            }
                            arg = entities.variable() || entities.property() || entities.literal() || entities.keyword() || this.call(true);
                        }

                        if (!arg || !hasSep) {
                            break;
                        }

                        nameLoop = null;
                        if (arg.throwAwayComments) {
                            arg.throwAwayComments();
                        }
                        value = arg;
                        var val = null;

                        if (isCall) {
                            // Variable
                            if (arg.value && arg.value.length == 1) {
                                val = arg.value[0];
                            }
                        } else {
                            val = arg;
                        }

                        if (val && (val instanceof tree.Variable || val instanceof tree.Property)) {
                            if (parserInput.$char(':')) {
                                if (expressions.length > 0) {
                                    if (isSemiColonSeparated) {
                                        error('Cannot mix ; and , as delimiter types');
                                    }
                                    expressionContainsNamed = true;
                                }

                                value = parsers.detachedRuleset() || parsers.expression();

                                if (!value) {
                                    if (isCall) {
                                        error('could not understand value for named argument');
                                    } else {
                                        parserInput.restore();
                                        returner.args = [];
                                        return returner;
                                    }
                                }
                                nameLoop = (name = val.name);
                            } else if (parserInput.$str('...')) {
                                if (!isCall) {
                                    returner.variadic = true;
                                    if (parserInput.$char(';') && !isSemiColonSeparated) {
                                        isSemiColonSeparated = true;
                                    }
                                    (isSemiColonSeparated ? argsSemiColon : argsComma)
                                        .push({ name: arg.name, variadic: true });
                                    break;
                                } else {
                                    expand = true;
                                }
                            } else if (!isCall) {
                                name = nameLoop = val.name;
                                value = null;
                            }
                        }

                        if (value) {
                            expressions.push(value);
                        }

                        argsComma.push({ name:nameLoop, value:value, expand:expand });

                        if (parserInput.$char(',')) {
                            hasSep = true;
                            continue;
                        }
                        hasSep = parserInput.$char(';') === ';';

                        if (hasSep || isSemiColonSeparated) {

                            if (expressionContainsNamed) {
                                error('Cannot mix ; and , as delimiter types');
                            }

                            isSemiColonSeparated = true;

                            if (expressions.length > 1) {
                                value = new(tree.Value)(expressions);
                            }
                            argsSemiColon.push({ name:name, value:value, expand:expand });

                            name = null;
                            expressions = [];
                            expressionContainsNamed = false;
                        }
                    }

                    parserInput.forget();
                    returner.args = isSemiColonSeparated ? argsSemiColon : argsComma;
                    return returner;
                },
                //
                // A Mixin definition, with a list of parameters
                //
                //     .rounded (@radius: 2px, @color) {
                //        ...
                //     }
                //
                // Until we have a finer grained state-machine, we have to
                // do a look-ahead, to make sure we don't have a mixin call.
                // See the `rule` function for more information.
                //
                // We start by matching `.rounded (`, and then proceed on to
                // the argument list, which has optional default values.
                // We store the parameters in `params`, with a `value` key,
                // if there is a value, such as in the case of `@radius`.
                //
                // Once we've got our params list, and a closing `)`, we parse
                // the `{...}` block.
                //
                definition: function () {
                    var name, params = [], match, ruleset, cond, variadic = false;
                    if ((parserInput.currentChar() !== '.' && parserInput.currentChar() !== '#') ||
                        parserInput.peek(/^[^{]*\}/)) {
                        return;
                    }

                    parserInput.save();

                    match = parserInput.$re(/^([#.](?:[\w-]|\\(?:[A-Fa-f0-9]{1,6} ?|[^A-Fa-f0-9]))+)\s*\(/);
                    if (match) {
                        name = match[1];

                        var argInfo = this.args(false);
                        params = argInfo.args;
                        variadic = argInfo.variadic;

                        // .mixincall("@{a}");
                        // looks a bit like a mixin definition..
                        // also
                        // .mixincall(@a: {rule: set;});
                        // so we have to be nice and restore
                        if (!parserInput.$char(')')) {
                            parserInput.restore('Missing closing \')\'');
                            return;
                        }

                        parserInput.commentStore.length = 0;

                        if (parserInput.$str('when')) { // Guard
                            cond = expect(parsers.conditions, 'expected condition');
                        }

                        ruleset = parsers.block();

                        if (ruleset) {
                            parserInput.forget();
                            return new(tree.mixin.Definition)(name, params, ruleset, cond, variadic);
                        } else {
                            parserInput.restore();
                        }
                    } else {
                        parserInput.forget();
                    }
                },
            
                ruleLookups: function() {
                    var rule, args, lookups = [];

                    if (parserInput.currentChar() !== '[') { 
                        return;
                    }
                    
                    while (true) {
                        parserInput.save();
                        args = null;
                        rule = this.lookupValue();
                        if (!rule && rule !== '') {
                            parserInput.restore();
                            break;
                        }
                        lookups.push(rule);
                        parserInput.forget();
                    }
                    if (lookups.length > 0) {
                        return lookups;
                    }
                },
    
                lookupValue: function() {
                    parserInput.save();
    
                    if (!parserInput.$char('[')) { 
                        parserInput.restore();
                        return;
                    }
    
                    var name = parserInput.$re(/^(?:[@$]{0,2})[_a-zA-Z0-9-]*/);
    
                    if (!parserInput.$char(']')) {
                        parserInput.restore();
                        return;
                    } 

                    if (name || name === '') {
                        parserInput.forget();
                        return name;
                    }
    
                    parserInput.restore();
                }
            },
            //
            // Entities are the smallest recognized token,
            // and can be found inside a rule's value.
            //
            entity: function () {
                var entities = this.entities;

                return this.comment() || entities.literal() || entities.variable() || entities.url() ||
                    entities.property() || entities.call() || entities.keyword() || this.mixin.call(true) ||
                    entities.javascript();
            },

            //
            // A Declaration terminator. Note that we use `peek()` to check for '}',
            // because the `block` rule will be expecting it, but we still need to make sure
            // it's there, if ';' was omitted.
            //
            end: function () {
                return parserInput.$char(';') || parserInput.peek('}');
            },

            //
            // IE's alpha function
            //
            //     alpha(opacity=88)
            //
            ieAlpha: function () {
                var value;

                // http://jsperf.com/case-insensitive-regex-vs-strtolower-then-regex/18
                if (!parserInput.$re(/^opacity=/i)) { return; }
                value = parserInput.$re(/^\d+/);
                if (!value) {
                    value = expect(parsers.entities.variable, 'Could not parse alpha');
                    value = '@{' + value.name.slice(1) + '}';
                }
                expectChar(')');
                return new tree.Quoted('', 'alpha(opacity=' + value + ')');
            },

            //
            // A Selector Element
            //
            //     div
            //     + h1
            //     #socks
            //     input[type="text"]
            //
            // Elements are the building blocks for Selectors,
            // they are made out of a `Combinator` (see combinator rule),
            // and an element name, such as a tag a class, or `*`.
            //
            element: function () {
                var e, c, v, index = parserInput.i;

                c = this.combinator();

                e = parserInput.$re(/^(?:\d+\.\d+|\d+)%/) ||
                    parserInput.$re(/^(?:[.#]?|:*)(?:[\w-]|[^\x00-\x9f]|\\(?:[A-Fa-f0-9]{1,6} ?|[^A-Fa-f0-9]))+/) ||
                    parserInput.$char('*') || parserInput.$char('&') || this.attribute() ||
                    parserInput.$re(/^\([^&()@]+\)/) ||  parserInput.$re(/^[\.#:](?=@)/) ||
                    this.entities.variableCurly();

                if (!e) {
                    parserInput.save();
                    if (parserInput.$char('(')) {
                        if ((v = this.selector(false)) && parserInput.$char(')')) {
                            e = new(tree.Paren)(v);
                            parserInput.forget();
                        } else {
                            parserInput.restore('Missing closing \')\'');
                        }
                    } else {
                        parserInput.forget();
                    }
                }

                if (e) { return new(tree.Element)(c, e, e instanceof tree.Variable, index, fileInfo); }
            },

            //
            // Combinators combine elements together, in a Selector.
            //
            // Because our parser isn't white-space sensitive, special care
            // has to be taken, when parsing the descendant combinator, ` `,
            // as it's an empty space. We have to check the previous character
            // in the input, to see if it's a ` ` character. More info on how
            // we deal with this in *combinator.js*.
            //
            combinator: function () {
                var c = parserInput.currentChar();

                if (c === '/') {
                    parserInput.save();
                    var slashedCombinator = parserInput.$re(/^\/[a-z]+\//i);
                    if (slashedCombinator) {
                        parserInput.forget();
                        return new(tree.Combinator)(slashedCombinator);
                    }
                    parserInput.restore();
                }

                if (c === '>' || c === '+' || c === '~' || c === '|' || c === '^') {
                    parserInput.i++;
                    if (c === '^' && parserInput.currentChar() === '^') {
                        c = '^^';
                        parserInput.i++;
                    }
                    while (parserInput.isWhitespace()) { parserInput.i++; }
                    return new(tree.Combinator)(c);
                } else if (parserInput.isWhitespace(-1)) {
                    return new(tree.Combinator)(' ');
                } else {
                    return new(tree.Combinator)(null);
                }
            },
            //
            // A CSS Selector
            // with less extensions e.g. the ability to extend and guard
            //
            //     .class > div + h1
            //     li a:hover
            //
            // Selectors are made out of one or more Elements, see above.
            //
            selector: function (isLess) {
                var index = parserInput.i, elements, extendList, c, e, allExtends, when, condition;
                isLess = isLess !== false;
                while ((isLess && (extendList = this.extend())) || (isLess && (when = parserInput.$str('when'))) || (e = this.element())) {
                    if (when) {
                        condition = expect(this.conditions, 'expected condition');
                    } else if (condition) {
                        error('CSS guard can only be used at the end of selector');
                    } else if (extendList) {
                        if (allExtends) {
                            allExtends = allExtends.concat(extendList);
                        } else {
                            allExtends = extendList;
                        }
                    } else {
                        if (allExtends) { error('Extend can only be used at the end of selector'); }
                        c = parserInput.currentChar();
                        if (elements) {
                            elements.push(e);
                        } else {
                            elements = [ e ];
                        }
                        e = null;
                    }
                    if (c === '{' || c === '}' || c === ';' || c === ',' || c === ')') {
                        break;
                    }
                }

                if (elements) { return new(tree.Selector)(elements, allExtends, condition, index, fileInfo); }
                if (allExtends) { error('Extend must be used to extend a selector, it cannot be used on its own'); }
            },
            selectors: function () {
                var s, selectors;
                while (true) {
                    s = this.selector();
                    if (!s) {
                        break;
                    }
                    if (selectors) {
                        selectors.push(s);
                    } else {
                        selectors = [ s ];
                    }
                    parserInput.commentStore.length = 0;
                    if (s.condition && selectors.length > 1) {
                        error("Guards are only currently allowed on a single selector.");
                    }
                    if (!parserInput.$char(',')) { break; }
                    if (s.condition) {
                        error("Guards are only currently allowed on a single selector.");
                    }
                    parserInput.commentStore.length = 0;
                }
                return selectors;
            },
            attribute: function () {
                if (!parserInput.$char('[')) { return; }

                var entities = this.entities,
                    key, val, op;

                if (!(key = entities.variableCurly())) {
                    key = expect(/^(?:[_A-Za-z0-9-\*]*\|)?(?:[_A-Za-z0-9-]|\\.)+/);
                }

                op = parserInput.$re(/^[|~*$^]?=/);
                if (op) {
                    val = entities.quoted() || parserInput.$re(/^[0-9]+%/) || parserInput.$re(/^[\w-]+/) || entities.variableCurly();
                }

                expectChar(']');

                return new(tree.Attribute)(key, op, val);
            },

            //
            // The `block` rule is used by `ruleset` and `mixin.definition`.
            // It's a wrapper around the `primary` rule, with added `{}`.
            //
            block: function () {
                var content;
                if (parserInput.$char('{') && (content = this.primary()) && parserInput.$char('}')) {
                    return content;
                }
            },

            blockRuleset: function() {
                var block = this.block();

                if (block) {
                    block = new tree.Ruleset(null, block);
                }
                return block;
            },

            detachedRuleset: function() {
                var argInfo, params, variadic;

                parserInput.save();
                if (parserInput.$re(/^[.#]\(/)) {
                    /**
                     * DR args currently only implemented for each() function, and not 
                     * yet settable as `@dr: #(@arg) {}`
                     * This should be done when DRs are merged with mixins.
                     * See: https://github.com/less/less-meta/issues/16
                     */
                    argInfo = this.mixin.args(false);
                    params = argInfo.args;
                    variadic = argInfo.variadic;
                    if (!parserInput.$char(')')) {
                        parserInput.restore();
                        return;
                    }
                }
                var blockRuleset = this.blockRuleset();
                if (blockRuleset) {
                    parserInput.forget();
                    if (params) {
                        return new tree.mixin.Definition(null, params, blockRuleset, null, variadic);
                    }
                    return new tree.DetachedRuleset(blockRuleset);
                }
                parserInput.restore();
            },

            //
            // div, .class, body > p {...}
            //
            ruleset: function () {
                var selectors, rules, debugInfo;

                parserInput.save();

                if (context.dumpLineNumbers) {
                    debugInfo = getDebugInfo(parserInput.i);
                }

                selectors = this.selectors();

                if (selectors && (rules = this.block())) {
                    parserInput.forget();
                    var ruleset = new(tree.Ruleset)(selectors, rules, context.strictImports);
                    if (context.dumpLineNumbers) {
                        ruleset.debugInfo = debugInfo;
                    }
                    return ruleset;
                } else {
                    parserInput.restore();
                }
            },
            declaration: function () {
                var name, value, index = parserInput.i, hasDR,
                    c = parserInput.currentChar(), important, merge, isVariable;

                if (c === '.' || c === '#' || c === '&' || c === ':') { return; }

                parserInput.save();

                name = this.variable() || this.ruleProperty();
                if (name) {
                    isVariable = typeof name === 'string';

                    if (isVariable) {
                        value = this.detachedRuleset();
                        if (value) {
                            hasDR = true;
                        }
                    }

                    parserInput.commentStore.length = 0;
                    if (!value) {
                        // a name returned by this.ruleProperty() is always an array of the form:
                        // [string-1, ..., string-n, ""] or [string-1, ..., string-n, "+"]
                        // where each item is a tree.Keyword or tree.Variable
                        merge = !isVariable && name.length > 1 && name.pop().value;

                        // Custom property values get permissive parsing
                        if (name[0].value && name[0].value.slice(0, 2) === '--') {
                            value = this.permissiveValue();
                        }
                        // Try to store values as anonymous
                        // If we need the value later we'll re-parse it in ruleset.parseValue
                        else {
                            value = this.anonymousValue();
                        }
                        if (value) {
                            parserInput.forget();
                            // anonymous values absorb the end ';' which is required for them to work
                            return new (tree.Declaration)(name, value, false, merge, index, fileInfo);
                        }

                        if (!value) {
                            value = this.value();
                        }

                        if (value) {
                            important = this.important();
                        } else if (isVariable) {
                            // As a last resort, try permissiveValue
                            value = this.permissiveValue();
                        }
                    }

                    if (value && (this.end() || hasDR)) {
                        parserInput.forget();
                        return new (tree.Declaration)(name, value, important, merge, index, fileInfo);
                    }
                    else {
                        parserInput.restore();
                    }
                } else {
                    parserInput.restore();
                }
            },
            anonymousValue: function () {
                var index = parserInput.i;
                var match = parserInput.$re(/^([^.#@\$+\/'"*`(;{}-]*);/);
                if (match) {
                    return new(tree.Anonymous)(match[1], index);
                }
            },
            /**
             * Used for custom properties, at-rules, and variables (as fallback)
             * Parses almost anything inside of {} [] () "" blocks
             * until it reaches outer-most tokens.
             * 
             * First, it will try to parse comments and entities to reach
             * the end. This is mostly like the Expression parser except no
             * math is allowed.
             */
            permissiveValue: function (untilTokens) {
                var i, e, done, value, 
                    tok = untilTokens || ';',
                    index = parserInput.i, result = [];

                function testCurrentChar() {
                    var char = parserInput.currentChar();
                    if (typeof tok === 'string') {
                        return char === tok;
                    } else {
                        return tok.test(char);
                    }
                }
                if (testCurrentChar()) {
                    return;
                }
                value = [];
                do {
                    e = this.comment();
                    if (e) {
                        value.push(e);
                        continue;
                    }
                    e = this.entity();
                    if (e) {
                        value.push(e);
                    }
                } while (e);

                done = testCurrentChar();
                
                if (value.length > 0) {
                    value = new(tree.Expression)(value);
                    if (done) {
                        return value;
                    }
                    else {
                        result.push(value);
                    }
                    // Preserve space before $parseUntil as it will not
                    if (parserInput.prevChar() === ' ') {
                        result.push(new tree.Anonymous(' ', index));
                    }
                }
                parserInput.save();
                
                value = parserInput.$parseUntil(tok);

                if (value) {
                    if (typeof value === 'string') {
                        error('Expected \'' + value + '\'', 'Parse');
                    }
                    if (value.length === 1 && value[0] === ' ') {
                        parserInput.forget();
                        return new tree.Anonymous('', index);
                    }
                    var item;
                    for (i = 0; i < value.length; i++) {
                        item = value[i];
                        if (Array.isArray(item)) {
                            // Treat actual quotes as normal quoted values
                            result.push(new tree.Quoted(item[0], item[1], true, index, fileInfo));
                        }
                        else {
                            if (i === value.length - 1) {
                                item = item.trim();
                            }
                            // Treat like quoted values, but replace vars like unquoted expressions
                            var quote = new tree.Quoted('\'', item, true, index, fileInfo);
                            quote.variableRegex = /@([\w-]+)/g;
                            quote.propRegex = /\$([\w-]+)/g;
                            result.push(quote);
                        }
                    }
                    parserInput.forget();
                    return new tree.Expression(result, true);
                }
                parserInput.restore();
            },

            //
            // An @import atrule
            //
            //     @import "lib";
            //
            // Depending on our environment, importing is done differently:
            // In the browser, it's an XHR request, in Node, it would be a
            // file-system operation. The function used for importing is
            // stored in `import`, which we pass to the Import constructor.
            //
            'import': function () {
                var path, features, index = parserInput.i;

                var dir = parserInput.$re(/^@import?\s+/);

                if (dir) {
                    var options = (dir ? this.importOptions() : null) || {};

                    if ((path = this.entities.quoted() || this.entities.url())) {
                        features = this.mediaFeatures();

                        if (!parserInput.$char(';')) {
                            parserInput.i = index;
                            error('missing semi-colon or unrecognised media features on import');
                        }
                        features = features && new(tree.Value)(features);
                        return new(tree.Import)(path, features, options, index, fileInfo);
                    }
                    else {
                        parserInput.i = index;
                        error('malformed import statement');
                    }
                }
            },

            importOptions: function() {
                var o, options = {}, optionName, value;

                // list of options, surrounded by parens
                if (!parserInput.$char('(')) { return null; }
                do {
                    o = this.importOption();
                    if (o) {
                        optionName = o;
                        value = true;
                        switch (optionName) {
                            case 'css':
                                optionName = 'less';
                                value = false;
                                break;
                            case 'once':
                                optionName = 'multiple';
                                value = false;
                                break;
                        }
                        options[optionName] = value;
                        if (!parserInput.$char(',')) { break; }
                    }
                } while (o);
                expectChar(')');
                return options;
            },

            importOption: function() {
                var opt = parserInput.$re(/^(less|css|multiple|once|inline|reference|optional)/);
                if (opt) {
                    return opt[1];
                }
            },

            mediaFeature: function () {
                var entities = this.entities, nodes = [], e, p;
                parserInput.save();
                do {
                    e = entities.keyword() || entities.variable() || entities.mixinLookup();
                    if (e) {
                        nodes.push(e);
                    } else if (parserInput.$char('(')) {
                        p = this.property();
                        e = this.value();
                        if (parserInput.$char(')')) {
                            if (p && e) {
                                nodes.push(new(tree.Paren)(new(tree.Declaration)(p, e, null, null, parserInput.i, fileInfo, true)));
                            } else if (e) {
                                nodes.push(new(tree.Paren)(e));
                            } else {
                                error('badly formed media feature definition');
                            }
                        } else {
                            error('Missing closing \')\'', 'Parse');
                        }
                    }
                } while (e);

                parserInput.forget();
                if (nodes.length > 0) {
                    return new(tree.Expression)(nodes);
                }
            },

            mediaFeatures: function () {
                var entities = this.entities, features = [], e;
                do {
                    e = this.mediaFeature();
                    if (e) {
                        features.push(e);
                        if (!parserInput.$char(',')) { break; }
                    } else {
                        e = entities.variable() || entities.mixinLookup();
                        if (e) {
                            features.push(e);
                            if (!parserInput.$char(',')) { break; }
                        }
                    }
                } while (e);

                return features.length > 0 ? features : null;
            },

            media: function () {
                var features, rules, media, debugInfo, index = parserInput.i;

                if (context.dumpLineNumbers) {
                    debugInfo = getDebugInfo(index);
                }

                parserInput.save();

                if (parserInput.$str('@media')) {
                    features = this.mediaFeatures();

                    rules = this.block();

                    if (!rules) {
                        error('media definitions require block statements after any features');
                    }

                    parserInput.forget();

                    media = new(tree.Media)(rules, features, index, fileInfo);
                    if (context.dumpLineNumbers) {
                        media.debugInfo = debugInfo;
                    }

                    return media;
                }

                parserInput.restore();
            },

            //

            // A @plugin directive, used to import plugins dynamically.
            //
            //     @plugin (args) "lib";
            //
            plugin: function () {
                var path, args, options,
                    index = parserInput.i,
                    dir   = parserInput.$re(/^@plugin?\s+/);

                if (dir) {
                    args = this.pluginArgs();

                    if (args) {
                        options = {
                            pluginArgs: args,
                            isPlugin: true
                        };
                    }
                    else {
                        options = { isPlugin: true };
                    }

                    if ((path = this.entities.quoted() || this.entities.url())) {

                        if (!parserInput.$char(';')) {
                            parserInput.i = index;
                            error('missing semi-colon on @plugin');
                        }
                        return new(tree.Import)(path, null, options, index, fileInfo);
                    }
                    else {
                        parserInput.i = index;
                        error('malformed @plugin statement');
                    }
                }
            },

            pluginArgs: function() {
                // list of options, surrounded by parens
                parserInput.save();
                if (!parserInput.$char('(')) {
                    parserInput.restore();
                    return null;
                }
                var args = parserInput.$re(/^\s*([^\);]+)\)\s*/);
                if (args[1]) {
                    parserInput.forget();
                    return args[1].trim();
                }
                else { 
                    parserInput.restore();
                    return null;
                }
            },

            //
            // A CSS AtRule
            //
            //     @charset "utf-8";
            //
            atrule: function () {
                var index = parserInput.i, name, value, rules, nonVendorSpecificName,
                    hasIdentifier, hasExpression, hasUnknown, hasBlock = true, isRooted = true;

                if (parserInput.currentChar() !== '@') { return; }

                value = this['import']() || this.plugin() || this.media();
                if (value) {
                    return value;
                }

                parserInput.save();

                name = parserInput.$re(/^@[a-z-]+/);

                if (!name) { return; }

                nonVendorSpecificName = name;
                if (name.charAt(1) == '-' && name.indexOf('-', 2) > 0) {
                    nonVendorSpecificName = '@' + name.slice(name.indexOf('-', 2) + 1);
                }

                switch (nonVendorSpecificName) {
                    case '@charset':
                        hasIdentifier = true;
                        hasBlock = false;
                        break;
                    case '@namespace':
                        hasExpression = true;
                        hasBlock = false;
                        break;
                    case '@keyframes':
                    case '@counter-style':
                        hasIdentifier = true;
                        break;
                    case '@document':
                    case '@supports':
                        hasUnknown = true;
                        isRooted = false;
                        break;
                    default:
                        hasUnknown = true;
                        break;
                }

                parserInput.commentStore.length = 0;

                if (hasIdentifier) {
                    value = this.entity();
                    if (!value) {
                        error('expected ' + name + ' identifier');
                    }
                } else if (hasExpression) {
                    value = this.expression();
                    if (!value) {
                        error('expected ' + name + ' expression');
                    }
                } else if (hasUnknown) {
                    value = this.permissiveValue(/^[{;]/);
                    hasBlock = (parserInput.currentChar() === '{');
                    if (!value) {
                        if (!hasBlock && parserInput.currentChar() !== ';') {
                            error(name + ' rule is missing block or ending semi-colon');
                        }
                    }
                    else if (!value.value) {
                        value = null;
                    }
                }

                if (hasBlock) {
                    rules = this.blockRuleset();
                }

                if (rules || (!hasBlock && value && parserInput.$char(';'))) {
                    parserInput.forget();
                    return new (tree.AtRule)(name, value, rules, index, fileInfo,
                        context.dumpLineNumbers ? getDebugInfo(index) : null,
                        isRooted
                    );
                }

                parserInput.restore('at-rule options not recognised');
            },

            //
            // A Value is a comma-delimited list of Expressions
            //
            //     font-family: Baskerville, Georgia, serif;
            //
            // In a Rule, a Value represents everything after the `:`,
            // and before the `;`.
            //
            value: function () {
                var e, expressions = [], index = parserInput.i;

                do {
                    e = this.expression();
                    if (e) {
                        expressions.push(e);
                        if (!parserInput.$char(',')) { break; }
                    }
                } while (e);

                if (expressions.length > 0) {
                    return new(tree.Value)(expressions, index);
                }
            },
            important: function () {
                if (parserInput.currentChar() === '!') {
                    return parserInput.$re(/^! *important/);
                }
            },
            sub: function () {
                var a, e;

                parserInput.save();
                if (parserInput.$char('(')) {
                    a = this.addition();
                    if (a && parserInput.$char(')')) {
                        parserInput.forget();
                        e = new(tree.Expression)([a]);
                        e.parens = true;
                        return e;
                    }
                    parserInput.restore('Expected \')\'');
                    return;
                }
                parserInput.restore();
            },
            multiplication: function () {
                var m, a, op, operation, isSpaced;
                m = this.operand();
                if (m) {
                    isSpaced = parserInput.isWhitespace(-1);
                    while (true) {
                        if (parserInput.peek(/^\/[*\/]/)) {
                            break;
                        }

                        parserInput.save();

                        op = parserInput.$char('/') || parserInput.$char('*') || parserInput.$str('./');

                        if (!op) { parserInput.forget(); break; }

                        a = this.operand();

                        if (!a) { parserInput.restore(); break; }
                        parserInput.forget();

                        m.parensInOp = true;
                        a.parensInOp = true;
                        operation = new(tree.Operation)(op, [operation || m, a], isSpaced);
                        isSpaced = parserInput.isWhitespace(-1);
                    }
                    return operation || m;
                }
            },
            addition: function () {
                var m, a, op, operation, isSpaced;
                m = this.multiplication();
                if (m) {
                    isSpaced = parserInput.isWhitespace(-1);
                    while (true) {
                        op = parserInput.$re(/^[-+]\s+/) || (!isSpaced && (parserInput.$char('+') || parserInput.$char('-')));
                        if (!op) {
                            break;
                        }
                        a = this.multiplication();
                        if (!a) {
                            break;
                        }

                        m.parensInOp = true;
                        a.parensInOp = true;
                        operation = new(tree.Operation)(op, [operation || m, a], isSpaced);
                        isSpaced = parserInput.isWhitespace(-1);
                    }
                    return operation || m;
                }
            },
            conditions: function () {
                var a, b, index = parserInput.i, condition;

                a = this.condition(true);
                if (a) {
                    while (true) {
                        if (!parserInput.peek(/^,\s*(not\s*)?\(/) || !parserInput.$char(',')) {
                            break;
                        }
                        b = this.condition(true);
                        if (!b) {
                            break;
                        }
                        condition = new(tree.Condition)('or', condition || a, b, index);
                    }
                    return condition || a;
                }
            },
            condition: function (needsParens) {
                var result, logical, next;
                function or() {
                    return parserInput.$str('or');
                }

                result = this.conditionAnd(needsParens);
                if (!result) {
                    return ;
                }
                logical = or();
                if (logical) {
                    next = this.condition(needsParens);
                    if (next) {
                        result = new(tree.Condition)(logical, result, next);
                    } else {
                        return ;
                    }
                }
                return result;
            },
            conditionAnd: function (needsParens) {
                var result, logical, next, self = this;
                function insideCondition() {
                    var cond = self.negatedCondition(needsParens) || self.parenthesisCondition(needsParens);
                    if (!cond && !needsParens) {
                        return self.atomicCondition(needsParens);
                    }
                    return cond;
                }
                function and() {
                    return parserInput.$str('and');
                }

                result = insideCondition();
                if (!result) {
                    return ;
                }
                logical = and();
                if (logical) {
                    next = this.conditionAnd(needsParens);
                    if (next) {
                        result = new(tree.Condition)(logical, result, next);
                    } else {
                        return ;
                    }
                }
                return result;
            },
            negatedCondition: function (needsParens) {
                if (parserInput.$str('not')) {
                    var result = this.parenthesisCondition(needsParens);
                    if (result) {
                        result.negate = !result.negate;
                    }
                    return result;
                }
            },
            parenthesisCondition: function (needsParens) {
                function tryConditionFollowedByParenthesis(me) {
                    var body;
                    parserInput.save();
                    body = me.condition(needsParens);
                    if (!body) {
                        parserInput.restore();
                        return ;
                    }
                    if (!parserInput.$char(')')) {
                        parserInput.restore();
                        return ;
                    }
                    parserInput.forget();
                    return body;
                }

                var body;
                parserInput.save();
                if (!parserInput.$str('(')) {
                    parserInput.restore();
                    return ;
                }
                body = tryConditionFollowedByParenthesis(this);
                if (body) {
                    parserInput.forget();
                    return body;
                }

                body = this.atomicCondition(needsParens);
                if (!body) {
                    parserInput.restore();
                    return ;
                }
                if (!parserInput.$char(')')) {
                    parserInput.restore('expected \')\' got \'' + parserInput.currentChar() + '\'');
                    return ;
                }
                parserInput.forget();
                return body;
            },
            atomicCondition: function (needsParens) {
                var entities = this.entities, index = parserInput.i, a, b, c, op;

                function cond() {
                    return this.addition() || entities.keyword() || entities.quoted() || entities.mixinLookup();
                }
                cond = cond.bind(this);

                a = cond();
                if (a) {
                    if (parserInput.$char('>')) {
                        if (parserInput.$char('=')) {
                            op = '>=';
                        } else {
                            op = '>';
                        }
                    } else
                    if (parserInput.$char('<')) {
                        if (parserInput.$char('=')) {
                            op = '<=';
                        } else {
                            op = '<';
                        }
                    } else
                    if (parserInput.$char('=')) {
                        if (parserInput.$char('>')) {
                            op = '=>';
                        } else if (parserInput.$char('<')) {
                            op = '=<';
                        } else {
                            op = '=';
                        }
                    }
                    if (op) {
                        b = cond();
                        if (b) {
                            c = new(tree.Condition)(op, a, b, index, false);
                        } else {
                            error('expected expression');
                        }
                    } else {
                        c = new(tree.Condition)('=', a, new(tree.Keyword)('true'), index, false);
                    }
                    return c;
                }
            },

            //
            // An operand is anything that can be part of an operation,
            // such as a Color, or a Variable
            //
            operand: function () {
                var entities = this.entities, negate;

                if (parserInput.peek(/^-[@\$\(]/)) {
                    negate = parserInput.$char('-');
                }

                var o = this.sub() || entities.dimension() ||
                        entities.color() || entities.variable() ||
                        entities.property() || entities.call() ||
                        entities.quoted(true) || entities.colorKeyword() ||
                        entities.mixinLookup();

                if (negate) {
                    o.parensInOp = true;
                    o = new(tree.Negative)(o);
                }

                return o;
            },

            //
            // Expressions either represent mathematical operations,
            // or white-space delimited Entities.
            //
            //     1px solid black
            //     @var * 2
            //
            expression: function () {
                var entities = [], e, delim, index = parserInput.i;

                do {
                    e = this.comment();
                    if (e) {
                        entities.push(e);
                        continue;
                    }
                    e = this.addition() || this.entity();
                    if (e) {
                        entities.push(e);
                        // operations do not allow keyword "/" dimension (e.g. small/20px) so we support that here
                        if (!parserInput.peek(/^\/[\/*]/)) {
                            delim = parserInput.$char('/');
                            if (delim) {
                                entities.push(new(tree.Anonymous)(delim, index));
                            }
                        }
                    }
                } while (e);
                if (entities.length > 0) {
                    return new(tree.Expression)(entities);
                }
            },
            property: function () {
                var name = parserInput.$re(/^(\*?-?[_a-zA-Z0-9-]+)\s*:/);
                if (name) {
                    return name[1];
                }
            },
            ruleProperty: function () {
                var name = [], index = [], s, k;

                parserInput.save();

                var simpleProperty = parserInput.$re(/^([_a-zA-Z0-9-]+)\s*:/);
                if (simpleProperty) {
                    name = [new(tree.Keyword)(simpleProperty[1])];
                    parserInput.forget();
                    return name;
                }

                function match(re) {
                    var i = parserInput.i,
                        chunk = parserInput.$re(re);
                    if (chunk) {
                        index.push(i);
                        return name.push(chunk[1]);
                    }
                }

                match(/^(\*?)/);
                while (true) {
                    if (!match(/^((?:[\w-]+)|(?:[@\$]\{[\w-]+\}))/)) {
                        break;
                    }
                }

                if ((name.length > 1) && match(/^((?:\+_|\+)?)\s*:/)) {
                    parserInput.forget();

                    // at last, we have the complete match now. move forward,
                    // convert name particles to tree objects and return:
                    if (name[0] === '') {
                        name.shift();
                        index.shift();
                    }
                    for (k = 0; k < name.length; k++) {
                        s = name[k];
                        name[k] = (s.charAt(0) !== '@' && s.charAt(0) !== '$') ?
                            new(tree.Keyword)(s) :
                            (s.charAt(0) === '@' ?
                                new(tree.Variable)('@' + s.slice(2, -1), index[k], fileInfo) :
                                new(tree.Property)('$' + s.slice(2, -1), index[k], fileInfo));
                    }
                    return name;
                }
                parserInput.restore();
            }
        }
    };
}
function Parser(context, imports, fileInfo) {
    var parsers,
        parserInput = getParserInput();

    function error(msg, type) {
        throw new LessError(
            {
                index: parserInput.i,
                filename: fileInfo.filename,
                type: type || 'Syntax',
                message: msg
            },
            imports
        );
    }

    function expect(arg, msg) {
        // some older browsers return typeof 'function' for RegExp
        var result = (arg instanceof Function) ? arg.call(parsers) : parserInput.$re(arg);
        if (result) {
            return result;
        }
        
        error(msg || (typeof arg === 'string'
            ? 'expected \'' + arg + '\' got \'' + parserInput.currentChar() + '\''
            : 'unexpected token'));
    }

    // Specialization of expect()
    function expectChar(arg, msg) {
        if (parserInput.$char(arg)) {
            return arg;
        }
        error(msg || 'expected \'' + arg + '\' got \'' + parserInput.currentChar() + '\'');
    }

    function getDebugInfo(index) {
        var filename = fileInfo.filename;

        return {
            lineNumber: utils.getLocation(index, parserInput.getInput()).line + 1,
            fileName: filename
        };
    }

    /**
     *  Used after initial parsing to create nodes on the fly
     * 
     *  @param {String} str          - string to parse 
     *  @param {Array}  parseList    - array of parsers to run input through e.g. ["value", "important"]
     *  @param {Number} currentIndex - start number to begin indexing
     *  @param {Object} fileInfo     - fileInfo to attach to created nodes
     */
    function parseNode(str, parseList, currentIndex, fileInfo, callback) {
        var result, returnNodes = [];
        var parser = parserInput;

        try {
            parser.start(str, false, function fail(msg, index) {
                callback({
                    message: msg,
                    index: index + currentIndex
                });
            });
            for (var x = 0, p, i; (p = parseList[x]); x++) {
                i = parser.i;
                result = parsers[p]();
                if (result) {
                    result._index = i + currentIndex;
                    result._fileInfo = fileInfo;
                    returnNodes.push(result);
                }
                else {
                    returnNodes.push(null);
                }
            }

            var endInfo = parser.end();
            if (endInfo.isFinished) {
                callback(null, returnNodes);
            }
            else {
                callback(true, null);
            }
        } catch (e) {
            throw new LessError({
                index: e.index + currentIndex,
                message: e.message
            }, imports, fileInfo.filename);
        }
    }
    
    //
    // The Parser
    //
    return {
        parserInput: parserInput,
        imports: imports,
        fileInfo: fileInfo,
        parseNode: parseNode,
        //
        // Parse an input string into an abstract syntax tree,
        // @param str A string containing 'less' markup
        // @param callback call `callback` when done.
        // @param [additionalData] An optional map which can contains vars - a map (key, value) of variables to apply
        //
        parse: function (str, callback, additionalData) {
            var root, error = null, globalVars, modifyVars, ignored, preText = '';

            globalVars = (additionalData && additionalData.globalVars) ? Parser.serializeVars(additionalData.globalVars) + '\n' : '';
            modifyVars = (additionalData && additionalData.modifyVars) ? '\n' + Parser.serializeVars(additionalData.modifyVars) : '';

            if (context.pluginManager) {
                var preProcessors = context.pluginManager.getPreProcessors();
                for (var i = 0; i < preProcessors.length; i++) {
                    str = preProcessors[i].process(str, { context: context, imports: imports, fileInfo: fileInfo });
                }
            }

            if (globalVars || (additionalData && additionalData.banner)) {
                preText = ((additionalData && additionalData.banner) ? additionalData.banner : '') + globalVars;
                ignored = imports.contentsIgnoredChars;
                ignored[fileInfo.filename] = ignored[fileInfo.filename] || 0;
                ignored[fileInfo.filename] += preText.length;
            }

            str = str.replace(/\r\n?/g, '\n');
            // Remove potential UTF Byte Order Mark
            str = preText + str.replace(/^\uFEFF/, '') + modifyVars;
            imports.contents[fileInfo.filename] = str;

            // Start with the primary rule.
            // The whole syntax tree is held under a Ruleset node,
            // with the `root` property set to true, so no `{}` are
            // output. The callback is called when the input is parsed.
            try {
                parserInput.start(str, context.chunkInput, function fail(msg, index) {
                    throw new LessError({
                        index: index,
                        type: 'Parse',
                        message: msg,
                        filename: fileInfo.filename
                    }, imports);
                });

                tree.Node.prototype.parse = this;
                root = new tree.Ruleset(null, this.parsers.primary());
                tree.Node.prototype.rootNode = root;
                root.root = true;
                root.firstRoot = true;
                root.functionRegistry = functionRegistry.inherit();
                
            } catch (e) {
                return callback(new LessError(e, imports, fileInfo.filename));
            }

            // If `i` is smaller than the `input.length - 1`,
            // it means the parser wasn't able to parse the whole
            // string, so we've got a parsing error.
            //
            // We try to extract a \n delimited string,
            // showing the line where the parse error occurred.
            // We split it up into two parts (the part which parsed,
            // and the part which didn't), so we can color them differently.
            var endInfo = parserInput.end();
            if (!endInfo.isFinished) {

                var message = endInfo.furthestPossibleErrorMessage;

                if (!message) {
                    message = 'Unrecognised input';
                    if (endInfo.furthestChar === '}') {
                        message += '. Possibly missing opening \'{\'';
                    } else if (endInfo.furthestChar === ')') {
                        message += '. Possibly missing opening \'(\'';
                    } else if (endInfo.furthestReachedEnd) {
                        message += '. Possibly missing something';
                    }
                }

                error = new LessError({
                    type: 'Parse',
                    message: message,
                    index: endInfo.furthest,
                    filename: fileInfo.filename
                }, imports);
            }

            var finish = function (e) {
                e = error || e || imports.error;

                if (e) {
                    if (!(e instanceof LessError)) {
                        e = new LessError(e, imports, fileInfo.filename);
                    }

                    return callback(e);
                }
                else {
                    return callback(null, root);
                }
            };

            if (context.processImports !== false) {
                new visitors.ImportVisitor(imports, finish)
                    .run(root);
            } else {
                return finish();
            }
        },

        //
        // Here in, the parsing rules/functions
        //
        // The basic structure of the syntax tree generated is as follows:
        //
        //   Ruleset ->  Declaration -> Value -> Expression -> Entity
        //
        // Here's some Less code:
        //
        //    .class {
        //      color: #fff;
        //      border: 1px solid #000;
        //      width: @w + 4px;
        //      > .child {...}
        //    }
        //
        // And here's what the parse tree might look like:
        //
        //     Ruleset (Selector '.class', [
        //         Declaration ("color",  Value ([Expression [Color #fff]]))
        //         Declaration ("border", Value ([Expression [Dimension 1px][Keyword "solid"][Color #000]]))
        //         Declaration ("width",  Value ([Expression [Operation " + " [Variable "@w"][Dimension 4px]]]))
        //         Ruleset (Selector [Element '>', '.child'], [...])
        //     ])
        //
        //  In general, most rules will try to parse a token with the `$re()` function, and if the return
        //  value is truly, will return a new node, of the relevant type. Sometimes, we need to check
        //  first, before parsing, that's when we use `peek()`.
        //
        parsers: parsers = {
            //
            // The `primary` rule is the *entry* and *exit* point of the parser.
            // The rules here can appear at any level of the parse tree.
            //
            // The recursive nature of the grammar is an interplay between the `block`
            // rule, which represents `{ ... }`, the `ruleset` rule, and this `primary` rule,
            // as represented by this simplified grammar:
            //
            //     primary  →  (ruleset | declaration)+
            //     ruleset  →  selector+ block
            //     block    →  '{' primary '}'
            //
            // Only at one point is the primary rule not called from the
            // block rule: at the root level.
            //
            primary: function () {
                var mixin = this.mixin, root = [], node;

                while (true) {
                    while (true) {
                        node = this.comment();
                        if (!node) { break; }
                        root.push(node);
                    }
                    // always process comments before deciding if finished
                    if (parserInput.finished) {
                        break;
                    }
                    if (parserInput.peek('}')) {
                        break;
                    }

                    node = this.extendRule();
                    if (node) {
                        root = root.concat(node);
                        continue;
                    }

                    node = mixin.definition() || this.declaration() || this.ruleset() ||
                        mixin.call(false, false) || this.variableCall() || this.entities.call() || this.atrule();
                    if (node) {
                        root.push(node);
                    } else {
                        var foundSemiColon = false;
                        while (parserInput.$char(';')) {
                            foundSemiColon = true;
                        }
                        if (!foundSemiColon) {
                            break;
                        }
                    }
                }

                return root;
            },

            // comments are collected by the main parsing mechanism and then assigned to nodes
            // where the current structure allows it
            comment: function () {
                if (parserInput.commentStore.length) {
                    var comment = parserInput.commentStore.shift();
                    return new(tree.Comment)(comment.text, comment.isLineComment, comment.index, fileInfo);
                }
            },

            //
            // Entities are tokens which can be found inside an Expression
            //
            entities: {
                mixinLookup: function() {
                    return parsers.mixin.call(true, true);
                },
                //
                // A string, which supports escaping " and '
                //
                //     "milky way" 'he\'s the one!'
                //
                quoted: function (forceEscaped) {
                    var str, index = parserInput.i, isEscaped = false;

                    parserInput.save();
                    if (parserInput.$char('~')) {
                        isEscaped = true;
                    } else if (forceEscaped) {
                        parserInput.restore();
                        return;
                    }

                    str = parserInput.$quoted();
                    if (!str) {
                        parserInput.restore();
                        return;
                    }
                    parserInput.forget();

                    return new(tree.Quoted)(str.charAt(0), str.substr(1, str.length - 2), isEscaped, index, fileInfo);
                },

                //
                // A catch-all word, such as:
                //
                //     black border-collapse
                //
                keyword: function () {
                    var k = parserInput.$char('%') || parserInput.$re(/^\[?(?:[\w-]|\\(?:[A-Fa-f0-9]{1,6} ?|[^A-Fa-f0-9]))+\]?/);
                    if (k) {
                        return tree.Color.fromKeyword(k) || new(tree.Keyword)(k);
                    }
                },

                //
                // A function call
                //
                //     rgb(255, 0, 255)
                //
                // The arguments are parsed with the `entities.arguments` parser.
                //
                call: function () {
                    var name, args, func, index = parserInput.i;

                    // http://jsperf.com/case-insensitive-regex-vs-strtolower-then-regex/18
                    if (parserInput.peek(/^url\(/i)) {
                        return;
                    }

                    parserInput.save();

                    name = parserInput.$re(/^([\w-]+|%|progid:[\w\.]+)\(/);
                    if (!name) {
                        parserInput.forget(); 
                        return;
                    }

                    name = name[1];
                    func = this.customFuncCall(name);
                    if (func) {
                        args = func.parse();
                        if (args && func.stop) {
                            parserInput.forget();
                            return args;
                        }
                    }

                    args = this.arguments(args);

                    if (!parserInput.$char(')')) {
                        parserInput.restore('Could not parse call arguments or missing \')\'');
                        return;
                    }

                    parserInput.forget();
                    
                    return new(tree.Call)(name, args, index, fileInfo);
                },
                
                //
                // Parsing rules for functions with non-standard args, e.g.:
                //
                //     boolean(not(2 > 1))
                //
                //     This is a quick prototype, to be modified/improved when
                //     more custom-parsed funcs come (e.g. `selector(...)`)
                //

                customFuncCall: function (name) {
                    /* Ideally the table is to be moved out of here for faster perf.,
                       but it's quite tricky since it relies on all these `parsers`
                       and `expect` available only here */
                    return {
                        alpha:   f(parsers.ieAlpha, true),
                        boolean: f(condition),
                        'if':    f(condition)
                    }[name.toLowerCase()];

                    function f(parse, stop) {
                        return {
                            parse: parse, // parsing function
                            stop:  stop   // when true - stop after parse() and return its result, 
                                          // otherwise continue for plain args
                        };
                    }
                
                    function condition() {
                        return [expect(parsers.condition, 'expected condition')];
                    }
                },

                arguments: function (prevArgs) {
                    var argsComma = prevArgs || [],
                        argsSemiColon = [],
                        isSemiColonSeparated, value;

                    parserInput.save();

                    while (true) {
                        if (prevArgs) {
                            prevArgs = false;
                        } else {
                            value = parsers.detachedRuleset() || this.assignment() || parsers.expression();
                            if (!value) {
                                break;
                            }

                            if (value.value && value.value.length == 1) {
                                value = value.value[0];
                            }

                            argsComma.push(value);
                        }

                        if (parserInput.$char(',')) {
                            continue;
                        }

                        if (parserInput.$char(';') || isSemiColonSeparated) {
                            isSemiColonSeparated = true;
                            value = (argsComma.length < 1) ? argsComma[0]
                                : new tree.Value(argsComma);
                            argsSemiColon.push(value);
                            argsComma = [];
                        }
                    }

                    parserInput.forget();
                    return isSemiColonSeparated ? argsSemiColon : argsComma;
                },
                literal: function () {
                    return this.dimension() ||
                           this.color() ||
                           this.quoted() ||
                           this.unicodeDescriptor();
                },

                // Assignments are argument entities for calls.
                // They are present in ie filter properties as shown below.
                //
                //     filter: progid:DXImageTransform.Microsoft.Alpha( *opacity=50* )
                //

                assignment: function () {
                    var key, value;
                    parserInput.save();
                    key = parserInput.$re(/^\w+(?=\s?=)/i);
                    if (!key) {
                        parserInput.restore();
                        return;
                    }
                    if (!parserInput.$char('=')) {
                        parserInput.restore();
                        return;
                    }
                    value = parsers.entity();
                    if (value) {
                        parserInput.forget();
                        return new(tree.Assignment)(key, value);
                    } else {
                        parserInput.restore();
                    }
                },

                //
                // Parse url() tokens
                //
                // We use a specific rule for urls, because they don't really behave like
                // standard function calls. The difference is that the argument doesn't have
                // to be enclosed within a string, so it can't be parsed as an Expression.
                //
                url: function () {
                    var value, index = parserInput.i;

                    parserInput.autoCommentAbsorb = false;

                    if (!parserInput.$str('url(')) {
                        parserInput.autoCommentAbsorb = true;
                        return;
                    }

                    value = this.quoted() || this.variable() || this.property() ||
                            parserInput.$re(/^(?:(?:\\[\(\)'"])|[^\(\)'"])+/) || '';

                    parserInput.autoCommentAbsorb = true;

                    expectChar(')');

                    return new(tree.URL)((value.value != null || 
                        value instanceof tree.Variable || 
                        value instanceof tree.Property) ?
                        value : new(tree.Anonymous)(value, index), index, fileInfo);
                },

                //
                // A Variable entity, such as `@fink`, in
                //
                //     width: @fink + 2px
                //
                // We use a different parser for variable definitions,
                // see `parsers.variable`.
                //
                variable: function () {
                    var ch, name, index = parserInput.i;

                    parserInput.save();
                    if (parserInput.currentChar() === '@' && (name = parserInput.$re(/^@@?[\w-]+/))) {
                        ch = parserInput.currentChar();
                        if (ch === '(' || ch === '[' && !parserInput.prevChar().match(/^\s/)) {
                            // this may be a VariableCall lookup
                            var result = parsers.variableCall(name);
                            if (result) {
                                parserInput.forget();
                                return result;
                            }
                        }
                        parserInput.forget();
                        return new(tree.Variable)(name, index, fileInfo);
                    }
                    parserInput.restore();
                },

                // A variable entity using the protective {} e.g. @{var}
                variableCurly: function () {
                    var curly, index = parserInput.i;

                    if (parserInput.currentChar() === '@' && (curly = parserInput.$re(/^@\{([\w-]+)\}/))) {
                        return new(tree.Variable)('@' + curly[1], index, fileInfo);
                    }
                },
                //
                // A Property accessor, such as `$color`, in
                //
                //     background-color: $color
                //
                property: function () {
                    var name, index = parserInput.i;

                    if (parserInput.currentChar() === '$' && (name = parserInput.$re(/^\$[\w-]+/))) {
                        return new(tree.Property)(name, index, fileInfo);
                    }
                },

                // A property entity useing the protective {} e.g. ${prop}
                propertyCurly: function () {
                    var curly, index = parserInput.i;

                    if (parserInput.currentChar() === '$' && (curly = parserInput.$re(/^\$\{([\w-]+)\}/))) {
                        return new(tree.Property)('$' + curly[1], index, fileInfo);
                    }
                },
                //
                // A Hexadecimal color
                //
                //     #4F3C2F
                //
                // `rgb` and `hsl` colors are parsed through the `entities.call` parser.
                //
                color: function () {
                    var rgb;

                    if (parserInput.currentChar() === '#' && (rgb = parserInput.$re(/^#([A-Fa-f0-9]{8}|[A-Fa-f0-9]{6}|[A-Fa-f0-9]{3,4})/))) {
                        return new(tree.Color)(rgb[1], undefined, rgb[0]);
                    }
                },

                colorKeyword: function () {
                    parserInput.save();
                    var autoCommentAbsorb = parserInput.autoCommentAbsorb;
                    parserInput.autoCommentAbsorb = false;
                    var k = parserInput.$re(/^[_A-Za-z-][_A-Za-z0-9-]+/);
                    parserInput.autoCommentAbsorb = autoCommentAbsorb;
                    if (!k) {
                        parserInput.forget();
                        return;
                    }
                    parserInput.restore();
                    var color = tree.Color.fromKeyword(k);
                    if (color) {
                        parserInput.$str(k);
                        return color;
                    }
                },

                //
                // A Dimension, that is, a number and a unit
                //
                //     0.5em 95%
                //
                dimension: function () {
                    if (parserInput.peekNotNumeric()) {
                        return;
                    }

                    var value = parserInput.$re(/^([+-]?\d*\.?\d+)(%|[a-z_]+)?/i);
                    if (value) {
                        return new(tree.Dimension)(value[1], value[2]);
                    }
                },

                //
                // A unicode descriptor, as is used in unicode-range
                //
                // U+0??  or U+00A1-00A9
                //
                unicodeDescriptor: function () {
                    var ud;

                    ud = parserInput.$re(/^U\+[0-9a-fA-F?]+(\-[0-9a-fA-F?]+)?/);
                    if (ud) {
                        return new(tree.UnicodeDescriptor)(ud[0]);
                    }
                },

                //
                // JavaScript code to be evaluated
                //
                //     `window.location.href`
                //
                javascript: function () {
                    var js, index = parserInput.i;

                    parserInput.save();

                    var escape = parserInput.$char('~');
                    var jsQuote = parserInput.$char('`');

                    if (!jsQuote) {
                        parserInput.restore();
                        return;
                    }

                    js = parserInput.$re(/^[^`]*`/);
                    if (js) {
                        parserInput.forget();
                        return new(tree.JavaScript)(js.substr(0, js.length - 1), Boolean(escape), index, fileInfo);
                    }
                    parserInput.restore('invalid javascript definition');
                }
            },

            //
            // The variable part of a variable definition. Used in the `rule` parser
            //
            //     @fink:
            //
            variable: function () {
                var name;

                if (parserInput.currentChar() === '@' && (name = parserInput.$re(/^(@[\w-]+)\s*:/))) { return name[1]; }
            },

            //
            // Call a variable value to retrieve a detached ruleset
            // or a value from a detached ruleset's rules.
            //
            //     @fink();
            //     @fink;
            //     color: @fink[@color];
            //
            variableCall: function (parsedName) {
                var lookups, important, i = parserInput.i,
                    inValue = !!parsedName, name = parsedName;

                parserInput.save();

                if (name || (parserInput.currentChar() === '@'
                    && (name = parserInput.$re(/^(@[\w-]+)(\(\s*\))?/)))) {

                    lookups = this.mixin.ruleLookups();

                    if (!lookups && ((inValue && parserInput.$str('()') !== '()') || (name[2] !== '()'))) {
                        parserInput.restore('Missing \'[...]\' lookup in variable call');
                        return;
                    }

                    if (!inValue) {
                        name = name[1];
                    }

                    if (lookups && parsers.important()) {
                        important = true;
                    }

                    var call = new tree.VariableCall(name, i, fileInfo);
                    if (!inValue && parsers.end()) {
                        parserInput.forget();
                        return call;
                    }
                    else {
                        parserInput.forget();
                        return new tree.NamespaceValue(call, lookups, important, i, fileInfo);
                    }
                }

                parserInput.restore();
            },

            //
            // extend syntax - used to extend selectors
            //
            extend: function(isRule) {
                var elements, e, index = parserInput.i, option, extendList, extend;

                if (!parserInput.$str(isRule ? '&:extend(' : ':extend(')) {
                    return;
                }

                do {
                    option = null;
                    elements = null;
                    while (!(option = parserInput.$re(/^(all)(?=\s*(\)|,))/))) {
                        e = this.element();
                        if (!e) {
                            break;
                        }
                        if (elements) {
                            elements.push(e);
                        } else {
                            elements = [ e ];
                        }
                    }

                    option = option && option[1];
                    if (!elements) {
                        error('Missing target selector for :extend().');
                    }
                    extend = new(tree.Extend)(new(tree.Selector)(elements), option, index, fileInfo);
                    if (extendList) {
                        extendList.push(extend);
                    } else {
                        extendList = [ extend ];
                    }
                } while (parserInput.$char(','));

                expect(/^\)/);

                if (isRule) {
                    expect(/^;/);
                }

                return extendList;
            },

            //
            // extendRule - used in a rule to extend all the parent selectors
            //
            extendRule: function() {
                return this.extend(true);
            },

            //
            // Mixins
            //
            mixin: {
                //
                // A Mixin call, with an optional argument list
                //
                //     #mixins > .square(#fff);
                //     #mixins.square(#fff);
                //     .rounded(4px, black);
                //     .button;
                //
                // We can lookup / return a value using the lookup syntax:
                //
                //     color: #mixin.square(#fff)[@color];
                //
                // The `while` loop is there because mixins can be
                // namespaced, but we only support the child and descendant
                // selector for now.
                //
                call: function (inValue, getLookup) {
                    var s = parserInput.currentChar(), important = false, lookups,
                        index = parserInput.i, elements, args, hasParens;

                    if (s !== '.' && s !== '#') { return; }

                    parserInput.save(); // stop us absorbing part of an invalid selector

                    elements = this.elements();

                    if (elements) {
                        if (parserInput.$char('(')) {
                            args = this.args(true).args;
                            expectChar(')');
                            hasParens = true;
                        }

                        if (getLookup !== false) {
                            lookups = this.ruleLookups();
                        }
                        if (getLookup === true && !lookups) {
                            parserInput.restore();
                            return;
                        }

                        if (inValue && !lookups && !hasParens) {
                            // This isn't a valid in-value mixin call
                            parserInput.restore();
                            return;
                        }

                        if (!inValue && parsers.important()) {
                            important = true;
                        }

                        if (inValue || parsers.end()) {
                            parserInput.forget();
                            var mixin = new(tree.mixin.Call)(elements, args, index, fileInfo, !lookups && important);
                            if (lookups) {
                                return new tree.NamespaceValue(mixin, lookups, important);
                            }
                            else {
                                return mixin;
                            }
                        }
                    }

                    parserInput.restore();
                },
                /**
                 * Matching elements for mixins
                 * (Start with . or # and can have > )
                 */
                elements: function() {
                    var elements, e, c, elem, elemIndex,
                        re = /^[#.](?:[\w-]|\\(?:[A-Fa-f0-9]{1,6} ?|[^A-Fa-f0-9]))+/;
                    while (true) {
                        elemIndex = parserInput.i;
                        e = parserInput.$re(re);
                        
                        if (!e) {
                            break;
                        }
                        elem = new(tree.Element)(c, e, false, elemIndex, fileInfo);
                        if (elements) {
                            elements.push(elem);
                        } else {
                            elements = [ elem ];
                        }
                        c = parserInput.$char('>');
                    }
                    return elements;
                },
                args: function (isCall) {
                    var entities = parsers.entities,
                        returner = { args:null, variadic: false },
                        expressions = [], argsSemiColon = [], argsComma = [],
                        isSemiColonSeparated, expressionContainsNamed, name, nameLoop,
                        value, arg, expand, hasSep = true; 

                    parserInput.save();

                    while (true) {
                        if (isCall) {
                            arg = parsers.detachedRuleset() || parsers.expression();
                        } else {
                            parserInput.commentStore.length = 0;
                            if (parserInput.$str('...')) {
                                returner.variadic = true;
                                if (parserInput.$char(';') && !isSemiColonSeparated) {
                                    isSemiColonSeparated = true;
                                }
                                (isSemiColonSeparated ? argsSemiColon : argsComma)
                                    .push({ variadic: true });
                                break;
                            }
                            arg = entities.variable() || entities.property() || entities.literal() || entities.keyword() || this.call(true);
                        }

                        if (!arg || !hasSep) {
                            break;
                        }

                        nameLoop = null;
                        if (arg.throwAwayComments) {
                            arg.throwAwayComments();
                        }
                        value = arg;
                        var val = null;

                        if (isCall) {
                            // Variable
                            if (arg.value && arg.value.length == 1) {
                                val = arg.value[0];
                            }
                        } else {
                            val = arg;
                        }

                        if (val && (val instanceof tree.Variable || val instanceof tree.Property)) {
                            if (parserInput.$char(':')) {
                                if (expressions.length > 0) {
                                    if (isSemiColonSeparated) {
                                        error('Cannot mix ; and , as delimiter types');
                                    }
                                    expressionContainsNamed = true;
                                }

                                value = parsers.detachedRuleset() || parsers.expression();

                                if (!value) {
                                    if (isCall) {
                                        error('could not understand value for named argument');
                                    } else {
                                        parserInput.restore();
                                        returner.args = [];
                                        return returner;
                                    }
                                }
                                nameLoop = (name = val.name);
                            } else if (parserInput.$str('...')) {
                                if (!isCall) {
                                    returner.variadic = true;
                                    if (parserInput.$char(';') && !isSemiColonSeparated) {
                                        isSemiColonSeparated = true;
                                    }
                                    (isSemiColonSeparated ? argsSemiColon : argsComma)
                                        .push({ name: arg.name, variadic: true });
                                    break;
                                } else {
                                    expand = true;
                                }
                            } else if (!isCall) {
                                name = nameLoop = val.name;
                                value = null;
                            }
                        }

                        if (value) {
                            expressions.push(value);
                        }

                        argsComma.push({ name:nameLoop, value:value, expand:expand });

                        if (parserInput.$char(',')) {
                            hasSep = true;
                            continue;
                        }
                        hasSep = parserInput.$char(';') === ';';

                        if (hasSep || isSemiColonSeparated) {

                            if (expressionContainsNamed) {
                                error('Cannot mix ; and , as delimiter types');
                            }

                            isSemiColonSeparated = true;

                            if (expressions.length > 1) {
                                value = new(tree.Value)(expressions);
                            }
                            argsSemiColon.push({ name:name, value:value, expand:expand });

                            name = null;
                            expressions = [];
                            expressionContainsNamed = false;
                        }
                    }

                    parserInput.forget();
                    returner.args = isSemiColonSeparated ? argsSemiColon : argsComma;
                    return returner;
                },
                //
                // A Mixin definition, with a list of parameters
                //
                //     .rounded (@radius: 2px, @color) {
                //        ...
                //     }
                //
                // Until we have a finer grained state-machine, we have to
                // do a look-ahead, to make sure we don't have a mixin call.
                // See the `rule` function for more information.
                //
                // We start by matching `.rounded (`, and then proceed on to
                // the argument list, which has optional default values.
                // We store the parameters in `params`, with a `value` key,
                // if there is a value, such as in the case of `@radius`.
                //
                // Once we've got our params list, and a closing `)`, we parse
                // the `{...}` block.
                //
                definition: function () {
                    var name, params = [], match, ruleset, cond, variadic = false;
                    if ((parserInput.currentChar() !== '.' && parserInput.currentChar() !== '#') ||
                        parserInput.peek(/^[^{]*\}/)) {
                        return;
                    }

                    parserInput.save();

                    match = parserInput.$re(/^([#.](?:[\w-]|\\(?:[A-Fa-f0-9]{1,6} ?|[^A-Fa-f0-9]))+)\s*\(/);
                    if (match) {
                        name = match[1];

                        var argInfo = this.args(false);
                        params = argInfo.args;
                        variadic = argInfo.variadic;

                        // .mixincall("@{a}");
                        // looks a bit like a mixin definition..
                        // also
                        // .mixincall(@a: {rule: set;});
                        // so we have to be nice and restore
                        if (!parserInput.$char(')')) {
                            parserInput.restore('Missing closing \')\'');
                            return;
                        }

                        parserInput.commentStore.length = 0;

                        if (parserInput.$str('when')) { // Guard
                            cond = expect(parsers.conditions, 'expected condition');
                        }

                        ruleset = parsers.block();

                        if (ruleset) {
                            parserInput.forget();
                            return new(tree.mixin.Definition)(name, params, ruleset, cond, variadic);
                        } else {
                            parserInput.restore();
                        }
                    } else {
                        parserInput.forget();
                    }
                },
            
                ruleLookups: function() {
                    var rule, args, lookups = [];

                    if (parserInput.currentChar() !== '[') { 
                        return;
                    }
                    
                    while (true) {
                        parserInput.save();
                        args = null;
                        rule = this.lookupValue();
                        if (!rule && rule !== '') {
                            parserInput.restore();
                            break;
                        }
                        lookups.push(rule);
                        parserInput.forget();
                    }
                    if (lookups.length > 0) {
                        return lookups;
                    }
                },
    
                lookupValue: function() {
                    parserInput.save();
    
                    if (!parserInput.$char('[')) { 
                        parserInput.restore();
                        return;
                    }
    
                    var name = parserInput.$re(/^(?:[@$]{0,2})[_a-zA-Z0-9-]*/);
    
                    if (!parserInput.$char(']')) {
                        parserInput.restore();
                        return;
                    } 

                    if (name || name === '') {
                        parserInput.forget();
                        return name;
                    }
    
                    parserInput.restore();
                }
            },
            //
            // Entities are the smallest recognized token,
            // and can be found inside a rule's value.
            //
            entity: function () {
                var entities = this.entities;

                return this.comment() || entities.literal() || entities.variable() || entities.url() ||
                    entities.property() || entities.call() || entities.keyword() || this.mixin.call(true) ||
                    entities.javascript();
            },

            //
            // A Declaration terminator. Note that we use `peek()` to check for '}',
            // because the `block` rule will be expecting it, but we still need to make sure
            // it's there, if ';' was omitted.
            //
            end: function () {
                return parserInput.$char(';') || parserInput.peek('}');
            },

            //
            // IE's alpha function
            //
            //     alpha(opacity=88)
            //
            ieAlpha: function () {
                var value;

                // http://jsperf.com/case-insensitive-regex-vs-strtolower-then-regex/18
                if (!parserInput.$re(/^opacity=/i)) { return; }
                value = parserInput.$re(/^\d+/);
                if (!value) {
                    value = expect(parsers.entities.variable, 'Could not parse alpha');
                    value = '@{' + value.name.slice(1) + '}';
                }
                expectChar(')');
                return new tree.Quoted('', 'alpha(opacity=' + value + ')');
            },

            //
            // A Selector Element
            //
            //     div
            //     + h1
            //     #socks
            //     input[type="text"]
            //
            // Elements are the building blocks for Selectors,
            // they are made out of a `Combinator` (see combinator rule),
            // and an element name, such as a tag a class, or `*`.
            //
            element: function () {
                var e, c, v, index = parserInput.i;

                c = this.combinator();

                e = parserInput.$re(/^(?:\d+\.\d+|\d+)%/) ||
                    parserInput.$re(/^(?:[.#]?|:*)(?:[\w-]|[^\x00-\x9f]|\\(?:[A-Fa-f0-9]{1,6} ?|[^A-Fa-f0-9]))+/) ||
                    parserInput.$char('*') || parserInput.$char('&') || this.attribute() ||
                    parserInput.$re(/^\([^&()@]+\)/) ||  parserInput.$re(/^[\.#:](?=@)/) ||
                    this.entities.variableCurly();

                if (!e) {
                    parserInput.save();
                    if (parserInput.$char('(')) {
                        if ((v = this.selector(false)) && parserInput.$char(')')) {
                            e = new(tree.Paren)(v);
                            parserInput.forget();
                        } else {
                            parserInput.restore('Missing closing \')\'');
                        }
                    } else {
                        parserInput.forget();
                    }
                }

                if (e) { return new(tree.Element)(c, e, e instanceof tree.Variable, index, fileInfo); }
            },

            //
            // Combinators combine elements together, in a Selector.
            //
            // Because our parser isn't white-space sensitive, special care
            // has to be taken, when parsing the descendant combinator, ` `,
            // as it's an empty space. We have to check the previous character
            // in the input, to see if it's a ` ` character. More info on how
            // we deal with this in *combinator.js*.
            //
            combinator: function () {
                var c = parserInput.currentChar();

                if (c === '/') {
                    parserInput.save();
                    var slashedCombinator = parserInput.$re(/^\/[a-z]+\//i);
                    if (slashedCombinator) {
                        parserInput.forget();
                        return new(tree.Combinator)(slashedCombinator);
                    }
                    parserInput.restore();
                }

                if (c === '>' || c === '+' || c === '~' || c === '|' || c === '^') {
                    parserInput.i++;
                    if (c === '^' && parserInput.currentChar() === '^') {
                        c = '^^';
                        parserInput.i++;
                    }
                    while (parserInput.isWhitespace()) { parserInput.i++; }
                    return new(tree.Combinator)(c);
                } else if (parserInput.isWhitespace(-1)) {
                    return new(tree.Combinator)(' ');
                } else {
                    return new(tree.Combinator)(null);
                }
            },
            //
            // A CSS Selector
            // with less extensions e.g. the ability to extend and guard
            //
            //     .class > div + h1
            //     li a:hover
            //
            // Selectors are made out of one or more Elements, see above.
            //
            selector: function (isLess) {
                var index = parserInput.i, elements, extendList, c, e, allExtends, when, condition;
                isLess = isLess !== false;
                while ((isLess && (extendList = this.extend())) || (isLess && (when = parserInput.$str('when'))) || (e = this.element())) {
                    if (when) {
                        condition = expect(this.conditions, 'expected condition');
                    } else if (condition) {
                        error('CSS guard can only be used at the end of selector');
                    } else if (extendList) {
                        if (allExtends) {
                            allExtends = allExtends.concat(extendList);
                        } else {
                            allExtends = extendList;
                        }
                    } else {
                        if (allExtends) { error('Extend can only be used at the end of selector'); }
                        c = parserInput.currentChar();
                        if (elements) {
                            elements.push(e);
                        } else {
                            elements = [ e ];
                        }
                        e = null;
                    }
                    if (c === '{' || c === '}' || c === ';' || c === ',' || c === ')') {
                        break;
                    }
                }

                if (elements) { return new(tree.Selector)(elements, allExtends, condition, index, fileInfo); }
                if (allExtends) { error('Extend must be used to extend a selector, it cannot be used on its own'); }
            },
            selectors: function () {
                var s, selectors;
                while (true) {
                    s = this.selector();
                    if (!s) {
                        break;
                    }
                    if (selectors) {
                        selectors.push(s);
                    } else {
                        selectors = [ s ];
                    }
                    parserInput.commentStore.length = 0;
                    if (s.condition && selectors.length > 1) {
                        error("Guards are only currently allowed on a single selector.");
                    }
                    if (!parserInput.$char(',')) { break; }
                    if (s.condition) {
                        error("Guards are only currently allowed on a single selector.");
                    }
                    parserInput.commentStore.length = 0;
                }
                return selectors;
            },
            attribute: function () {
                if (!parserInput.$char('[')) { return; }

                var entities = this.entities,
                    key, val, op;

                if (!(key = entities.variableCurly())) {
                    key = expect(/^(?:[_A-Za-z0-9-\*]*\|)?(?:[_A-Za-z0-9-]|\\.)+/);
                }

                op = parserInput.$re(/^[|~*$^]?=/);
                if (op) {
                    val = entities.quoted() || parserInput.$re(/^[0-9]+%/) || parserInput.$re(/^[\w-]+/) || entities.variableCurly();
                }

                expectChar(']');

                return new(tree.Attribute)(key, op, val);
            },

            //
            // The `block` rule is used by `ruleset` and `mixin.definition`.
            // It's a wrapper around the `primary` rule, with added `{}`.
            //
            block: function () {
                var content;
                if (parserInput.$char('{') && (content = this.primary()) && parserInput.$char('}')) {
                    return content;
                }
            },

            blockRuleset: function() {
                var block = this.block();

                if (block) {
                    block = new tree.Ruleset(null, block);
                }
                return block;
            },

            detachedRuleset: function() {
                var argInfo, params, variadic;

                parserInput.save();
                if (parserInput.$re(/^[.#]\(/)) {
                    /**
                     * DR args currently only implemented for each() function, and not 
                     * yet settable as `@dr: #(@arg) {}`
                     * This should be done when DRs are merged with mixins.
                     * See: https://github.com/less/less-meta/issues/16
                     */
                    argInfo = this.mixin.args(false);
                    params = argInfo.args;
                    variadic = argInfo.variadic;
                    if (!parserInput.$char(')')) {
                        parserInput.restore();
                        return;
                    }
                }
                var blockRuleset = this.blockRuleset();
                if (blockRuleset) {
                    parserInput.forget();
                    if (params) {
                        return new tree.mixin.Definition(null, params, blockRuleset, null, variadic);
                    }
                    return new tree.DetachedRuleset(blockRuleset);
                }
                parserInput.restore();
            },

            //
            // div, .class, body > p {...}
            //
            ruleset: function () {
                var selectors, rules, debugInfo;

                parserInput.save();

                if (context.dumpLineNumbers) {
                    debugInfo = getDebugInfo(parserInput.i);
                }

                selectors = this.selectors();

                if (selectors && (rules = this.block())) {
                    parserInput.forget();
                    var ruleset = new(tree.Ruleset)(selectors, rules, context.strictImports);
                    if (context.dumpLineNumbers) {
                        ruleset.debugInfo = debugInfo;
                    }
                    return ruleset;
                } else {
                    parserInput.restore();
                }
            },
            declaration: function () {
                var name, value, index = parserInput.i, hasDR,
                    c = parserInput.currentChar(), important, merge, isVariable;

                if (c === '.' || c === '#' || c === '&' || c === ':') { return; }

                parserInput.save();

                name = this.variable() || this.ruleProperty();
                if (name) {
                    isVariable = typeof name === 'string';

                    if (isVariable) {
                        value = this.detachedRuleset();
                        if (value) {
                            hasDR = true;
                        }
                    }

                    parserInput.commentStore.length = 0;
                    if (!value) {
                        // a name returned by this.ruleProperty() is always an array of the form:
                        // [string-1, ..., string-n, ""] or [string-1, ..., string-n, "+"]
                        // where each item is a tree.Keyword or tree.Variable
                        merge = !isVariable && name.length > 1 && name.pop().value;

                        // Custom property values get permissive parsing
                        if (name[0].value && name[0].value.slice(0, 2) === '--') {
                            value = this.permissiveValue();
                        }
                        // Try to store values as anonymous
                        // If we need the value later we'll re-parse it in ruleset.parseValue
                        else {
                            value = this.anonymousValue();
                        }
                        if (value) {
                            parserInput.forget();
                            // anonymous values absorb the end ';' which is required for them to work
                            return new (tree.Declaration)(name, value, false, merge, index, fileInfo);
                        }

                        if (!value) {
                            value = this.value();
                        }

                        if (value) {
                            important = this.important();
                        } else if (isVariable) {
                            // As a last resort, try permissiveValue
                            value = this.permissiveValue();
                        }
                    }

                    if (value && (this.end() || hasDR)) {
                        parserInput.forget();
                        return new (tree.Declaration)(name, value, important, merge, index, fileInfo);
                    }
                    else {
                        parserInput.restore();
                    }
                } else {
                    parserInput.restore();
                }
            },
            anonymousValue: function () {
                var index = parserInput.i;
                var match = parserInput.$re(/^([^.#@\$+\/'"*`(;{}-]*);/);
                if (match) {
                    return new(tree.Anonymous)(match[1], index);
                }
            },
            /**
             * Used for custom properties, at-rules, and variables (as fallback)
             * Parses almost anything inside of {} [] () "" blocks
             * until it reaches outer-most tokens.
             * 
             * First, it will try to parse comments and entities to reach
             * the end. This is mostly like the Expression parser except no
             * math is allowed.
             */
            permissiveValue: function (untilTokens) {
                var i, e, done, value, 
                    tok = untilTokens || ';',
                    index = parserInput.i, result = [];

                function testCurrentChar() {
                    var char = parserInput.currentChar();
                    if (typeof tok === 'string') {
                        return char === tok;
                    } else {
                        return tok.test(char);
                    }
                }
                if (testCurrentChar()) {
                    return;
                }
                value = [];
                do {
                    e = this.comment();
                    if (e) {
                        value.push(e);
                        continue;
                    }
                    e = this.entity();
                    if (e) {
                        value.push(e);
                    }
                } while (e);

                done = testCurrentChar();
                
                if (value.length > 0) {
                    value = new(tree.Expression)(value);
                    if (done) {
                        return value;
                    }
                    else {
                        result.push(value);
                    }
                    // Preserve space before $parseUntil as it will not
                    if (parserInput.prevChar() === ' ') {
                        result.push(new tree.Anonymous(' ', index));
                    }
                }
                parserInput.save();
                
                value = parserInput.$parseUntil(tok);

                if (value) {
                    if (typeof value === 'string') {
                        error('Expected \'' + value + '\'', 'Parse');
                    }
                    if (value.length === 1 && value[0] === ' ') {
                        parserInput.forget();
                        return new tree.Anonymous('', index);
                    }
                    var item;
                    for (i = 0; i < value.length; i++) {
                        item = value[i];
                        if (Array.isArray(item)) {
                            // Treat actual quotes as normal quoted values
                            result.push(new tree.Quoted(item[0], item[1], true, index, fileInfo));
                        }
                        else {
                            if (i === value.length - 1) {
                                item = item.trim();
                            }
                            // Treat like quoted values, but replace vars like unquoted expressions
                            var quote = new tree.Quoted('\'', item, true, index, fileInfo);
                            quote.variableRegex = /@([\w-]+)/g;
                            quote.propRegex = /\$([\w-]+)/g;
                            result.push(quote);
                        }
                    }
                    parserInput.forget();
                    return new tree.Expression(result, true);
                }
                parserInput.restore();
            },

            //
            // An @import atrule
            //
            //     @import "lib";
            //
            // Depending on our environment, importing is done differently:
            // In the browser, it's an XHR request, in Node, it would be a
            // file-system operation. The function used for importing is
            // stored in `import`, which we pass to the Import constructor.
            //
            'import': function () {
                var path, features, index = parserInput.i;

                var dir = parserInput.$re(/^@import?\s+/);

                if (dir) {
                    var options = (dir ? this.importOptions() : null) || {};

                    if ((path = this.entities.quoted() || this.entities.url())) {
                        features = this.mediaFeatures();

                        if (!parserInput.$char(';')) {
                            parserInput.i = index;
                            error('missing semi-colon or unrecognised media features on import');
                        }
                        features = features && new(tree.Value)(features);
                        return new(tree.Import)(path, features, options, index, fileInfo);
                    }
                    else {
                        parserInput.i = index;
                        error('malformed import statement');
                    }
                }
            },

            importOptions: function() {
                var o, options = {}, optionName, value;

                // list of options, surrounded by parens
                if (!parserInput.$char('(')) { return null; }
                do {
                    o = this.importOption();
                    if (o) {
                        optionName = o;
                        value = true;
                        switch (optionName) {
                            case 'css':
                                optionName = 'less';
                                value = false;
                                break;
                            case 'once':
                                optionName = 'multiple';
                                value = false;
                                break;
                        }
                        options[optionName] = value;
                        if (!parserInput.$char(',')) { break; }
                    }
                } while (o);
                expectChar(')');
                return options;
            },

            importOption: function() {
                var opt = parserInput.$re(/^(less|css|multiple|once|inline|reference|optional)/);
                if (opt) {
                    return opt[1];
                }
            },

            mediaFeature: function () {
                var entities = this.entities, nodes = [], e, p;
                parserInput.save();
                do {
                    e = entities.keyword() || entities.variable() || entities.mixinLookup();
                    if (e) {
                        nodes.push(e);
                    } else if (parserInput.$char('(')) {
                        p = this.property();
                        e = this.value();
                        if (parserInput.$char(')')) {
                            if (p && e) {
                                nodes.push(new(tree.Paren)(new(tree.Declaration)(p, e, null, null, parserInput.i, fileInfo, true)));
                            } else if (e) {
                                nodes.push(new(tree.Paren)(e));
                            } else {
                                error('badly formed media feature definition');
                            }
                        } else {
                            error('Missing closing \')\'', 'Parse');
                        }
                    }
                } while (e);

                parserInput.forget();
                if (nodes.length > 0) {
                    return new(tree.Expression)(nodes);
                }
            },

            mediaFeatures: function () {
                var entities = this.entities, features = [], e;
                do {
                    e = this.mediaFeature();
                    if (e) {
                        features.push(e);
                        if (!parserInput.$char(',')) { break; }
                    } else {
                        e = entities.variable() || entities.mixinLookup();
                        if (e) {
                            features.push(e);
                            if (!parserInput.$char(',')) { break; }
                        }
                    }
                } while (e);

                return features.length > 0 ? features : null;
            },

            media: function () {
                var features, rules, media, debugInfo, index = parserInput.i;

                if (context.dumpLineNumbers) {
                    debugInfo = getDebugInfo(index);
                }

                parserInput.save();

                if (parserInput.$str('@media')) {
                    features = this.mediaFeatures();

                    rules = this.block();

                    if (!rules) {
                        error('media definitions require block statements after any features');
                    }

                    parserInput.forget();

                    media = new(tree.Media)(rules, features, index, fileInfo);
                    if (context.dumpLineNumbers) {
                        media.debugInfo = debugInfo;
                    }

                    return media;
                }

                parserInput.restore();
            },

            //

            // A @plugin directive, used to import plugins dynamically.
            //
            //     @plugin (args) "lib";
            //
            plugin: function () {
                var path, args, options,
                    index = parserInput.i,
                    dir   = parserInput.$re(/^@plugin?\s+/);

                if (dir) {
                    args = this.pluginArgs();

                    if (args) {
                        options = {
                            pluginArgs: args,
                            isPlugin: true
                        };
                    }
                    else {
                        options = { isPlugin: true };
                    }

                    if ((path = this.entities.quoted() || this.entities.url())) {

                        if (!parserInput.$char(';')) {
                            parserInput.i = index;
                            error('missing semi-colon on @plugin');
                        }
                        return new(tree.Import)(path, null, options, index, fileInfo);
                    }
                    else {
                        parserInput.i = index;
                        error('malformed @plugin statement');
                    }
                }
            },

            pluginArgs: function() {
                // list of options, surrounded by parens
                parserInput.save();
                if (!parserInput.$char('(')) {
                    parserInput.restore();
                    return null;
                }
                var args = parserInput.$re(/^\s*([^\);]+)\)\s*/);
                if (args[1]) {
                    parserInput.forget();
                    return args[1].trim();
                }
                else { 
                    parserInput.restore();
                    return null;
                }
            },

            //
            // A CSS AtRule
            //
            //     @charset "utf-8";
            //
            atrule: function () {
                var index = parserInput.i, name, value, rules, nonVendorSpecificName,
                    hasIdentifier, hasExpression, hasUnknown, hasBlock = true, isRooted = true;

                if (parserInput.currentChar() !== '@') { return; }

                value = this['import']() || this.plugin() || this.media();
                if (value) {
                    return value;
                }

                parserInput.save();

                name = parserInput.$re(/^@[a-z-]+/);

                if (!name) { return; }

                nonVendorSpecificName = name;
                if (name.charAt(1) == '-' && name.indexOf('-', 2) > 0) {
                    nonVendorSpecificName = '@' + name.slice(name.indexOf('-', 2) + 1);
                }

                switch (nonVendorSpecificName) {
                    case '@charset':
                        hasIdentifier = true;
                        hasBlock = false;
                        break;
                    case '@namespace':
                        hasExpression = true;
                        hasBlock = false;
                        break;
                    case '@keyframes':
                    case '@counter-style':
                        hasIdentifier = true;
                        break;
                    case '@document':
                    case '@supports':
                        hasUnknown = true;
                        isRooted = false;
                        break;
                    default:
                        hasUnknown = true;
                        break;
                }

                parserInput.commentStore.length = 0;

                if (hasIdentifier) {
                    value = this.entity();
                    if (!value) {
                        error('expected ' + name + ' identifier');
                    }
                } else if (hasExpression) {
                    value = this.expression();
                    if (!value) {
                        error('expected ' + name + ' expression');
                    }
                } else if (hasUnknown) {
                    value = this.permissiveValue(/^[{;]/);
                    hasBlock = (parserInput.currentChar() === '{');
                    if (!value) {
                        if (!hasBlock && parserInput.currentChar() !== ';') {
                            error(name + ' rule is missing block or ending semi-colon');
                        }
                    }
                    else if (!value.value) {
                        value = null;
                    }
                }

                if (hasBlock) {
                    rules = this.blockRuleset();
                }

                if (rules || (!hasBlock && value && parserInput.$char(';'))) {
                    parserInput.forget();
                    return new (tree.AtRule)(name, value, rules, index, fileInfo,
                        context.dumpLineNumbers ? getDebugInfo(index) : null,
                        isRooted
                    );
                }

                parserInput.restore('at-rule options not recognised');
            },

            //
            // A Value is a comma-delimited list of Expressions
            //
            //     font-family: Baskerville, Georgia, serif;
            //
            // In a Rule, a Value represents everything after the `:`,
            // and before the `;`.
            //
            value: function () {
                var e, expressions = [], index = parserInput.i;

                do {
                    e = this.expression();
                    if (e) {
                        expressions.push(e);
                        if (!parserInput.$char(',')) { break; }
                    }
                } while (e);

                if (expressions.length > 0) {
                    return new(tree.Value)(expressions, index);
                }
            },
            important: function () {
                if (parserInput.currentChar() === '!') {
                    return parserInput.$re(/^! *important/);
                }
            },
            sub: function () {
                var a, e;

                parserInput.save();
                if (parserInput.$char('(')) {
                    a = this.addition();
                    if (a && parserInput.$char(')')) {
                        parserInput.forget();
                        e = new(tree.Expression)([a]);
                        e.parens = true;
                        return e;
                    }
                    parserInput.restore('Expected \')\'');
                    return;
                }
                parserInput.restore();
            },
            multiplication: function () {
                var m, a, op, operation, isSpaced;
                m = this.operand();
                if (m) {
                    isSpaced = parserInput.isWhitespace(-1);
                    while (true) {
                        if (parserInput.peek(/^\/[*\/]/)) {
                            break;
                        }

                        parserInput.save();

                        op = parserInput.$char('/') || parserInput.$char('*') || parserInput.$str('./');

                        if (!op) { parserInput.forget(); break; }

                        a = this.operand();

                        if (!a) { parserInput.restore(); break; }
                        parserInput.forget();

                        m.parensInOp = true;
                        a.parensInOp = true;
                        operation = new(tree.Operation)(op, [operation || m, a], isSpaced);
                        isSpaced = parserInput.isWhitespace(-1);
                    }
                    return operation || m;
                }
            },
            addition: function () {
                var m, a, op, operation, isSpaced;
                m = this.multiplication();
                if (m) {
                    isSpaced = parserInput.isWhitespace(-1);
                    while (true) {
                        op = parserInput.$re(/^[-+]\s+/) || (!isSpaced && (parserInput.$char('+') || parserInput.$char('-')));
                        if (!op) {
                            break;
                        }
                        a = this.multiplication();
                        if (!a) {
                            break;
                        }

                        m.parensInOp = true;
                        a.parensInOp = true;
                        operation = new(tree.Operation)(op, [operation || m, a], isSpaced);
                        isSpaced = parserInput.isWhitespace(-1);
                    }
                    return operation || m;
                }
            },
            conditions: function () {
                var a, b, index = parserInput.i, condition;

                a = this.condition(true);
                if (a) {
                    while (true) {
                        if (!parserInput.peek(/^,\s*(not\s*)?\(/) || !parserInput.$char(',')) {
                            break;
                        }
                        b = this.condition(true);
                        if (!b) {
                            break;
                        }
                        condition = new(tree.Condition)('or', condition || a, b, index);
                    }
                    return condition || a;
                }
            },
            condition: function (needsParens) {
                var result, logical, next;
                function or() {
                    return parserInput.$str('or');
                }

                result = this.conditionAnd(needsParens);
                if (!result) {
                    return ;
                }
                logical = or();
                if (logical) {
                    next = this.condition(needsParens);
                    if (next) {
                        result = new(tree.Condition)(logical, result, next);
                    } else {
                        return ;
                    }
                }
                return result;
            },
            conditionAnd: function (needsParens) {
                var result, logical, next, self = this;
                function insideCondition() {
                    var cond = self.negatedCondition(needsParens) || self.parenthesisCondition(needsParens);
                    if (!cond && !needsParens) {
                        return self.atomicCondition(needsParens);
                    }
                    return cond;
                }
                function and() {
                    return parserInput.$str('and');
                }

                result = insideCondition();
                if (!result) {
                    return ;
                }
                logical = and();
                if (logical) {
                    next = this.conditionAnd(needsParens);
                    if (next) {
                        result = new(tree.Condition)(logical, result, next);
                    } else {
                        return ;
                    }
                }
                return result;
            },
            negatedCondition: function (needsParens) {
                if (parserInput.$str('not')) {
                    var result = this.parenthesisCondition(needsParens);
                    if (result) {
                        result.negate = !result.negate;
                    }
                    return result;
                }
            },
            parenthesisCondition: function (needsParens) {
                function tryConditionFollowedByParenthesis(me) {
                    var body;
                    parserInput.save();
                    body = me.condition(needsParens);
                    if (!body) {
                        parserInput.restore();
                        return ;
                    }
                    if (!parserInput.$char(')')) {
                        parserInput.restore();
                        return ;
                    }
                    parserInput.forget();
                    return body;
                }

                var body;
                parserInput.save();
                if (!parserInput.$str('(')) {
                    parserInput.restore();
                    return ;
                }
                body = tryConditionFollowedByParenthesis(this);
                if (body) {
                    parserInput.forget();
                    return body;
                }

                body = this.atomicCondition(needsParens);
                if (!body) {
                    parserInput.restore();
                    return ;
                }
                if (!parserInput.$char(')')) {
                    parserInput.restore('expected \')\' got \'' + parserInput.currentChar() + '\'');
                    return ;
                }
                parserInput.forget();
                return body;
            },
            atomicCondition: function (needsParens) {
                var entities = this.entities, index = parserInput.i, a, b, c, op;

                function cond() {
                    return this.addition() || entities.keyword() || entities.quoted() || entities.mixinLookup();
                }
                cond = cond.bind(this);

                a = cond();
                if (a) {
                    if (parserInput.$char('>')) {
                        if (parserInput.$char('=')) {
                            op = '>=';
                        } else {
                            op = '>';
                        }
                    } else
                    if (parserInput.$char('<')) {
                        if (parserInput.$char('=')) {
                            op = '<=';
                        } else {
                            op = '<';
                        }
                    } else
                    if (parserInput.$char('=')) {
                        if (parserInput.$char('>')) {
                            op = '=>';
                        } else if (parserInput.$char('<')) {
                            op = '=<';
                        } else {
                            op = '=';
                        }
                    }
                    if (op) {
                        b = cond();
                        if (b) {
                            c = new(tree.Condition)(op, a, b, index, false);
                        } else {
                            error('expected expression');
                        }
                    } else {
                        c = new(tree.Condition)('=', a, new(tree.Keyword)('true'), index, false);
                    }
                    return c;
                }
            },

            //
            // An operand is anything that can be part of an operation,
            // such as a Color, or a Variable
            //
            operand: function () {
                var entities = this.entities, negate;

                if (parserInput.peek(/^-[@\$\(]/)) {
                    negate = parserInput.$char('-');
                }

                var o = this.sub() || entities.dimension() ||
                        entities.color() || entities.variable() ||
                        entities.property() || entities.call() ||
                        entities.quoted(true) || entities.colorKeyword() ||
                        entities.mixinLookup();

                if (negate) {
                    o.parensInOp = true;
                    o = new(tree.Negative)(o);
                }

                return o;
            },

            //
            // Expressions either represent mathematical operations,
            // or white-space delimited Entities.
            //
            //     1px solid black
            //     @var * 2
            //
            expression: function () {
                var entities = [], e, delim, index = parserInput.i;

                do {
                    e = this.comment();
                    if (e) {
                        entities.push(e);
                        continue;
                    }
                    e = this.addition() || this.entity();
                    if (e) {
                        entities.push(e);
                        // operations do not allow keyword "/" dimension (e.g. small/20px) so we support that here
                        if (!parserInput.peek(/^\/[\/*]/)) {
                            delim = parserInput.$char('/');
                            if (delim) {
                                entities.push(new(tree.Anonymous)(delim, index));
                            }
                        }
                    }
                } while (e);
                if (entities.length > 0) {
                    return new(tree.Expression)(entities);
                }
            },
            property: function () {
                var name = parserInput.$re(/^(\*?-?[_a-zA-Z0-9-]+)\s*:/);
                if (name) {
                    return name[1];
                }
            },
            ruleProperty: function () {
                var name = [], index = [], s, k;

                parserInput.save();

                var simpleProperty = parserInput.$re(/^([_a-zA-Z0-9-]+)\s*:/);
                if (simpleProperty) {
                    name = [new(tree.Keyword)(simpleProperty[1])];
                    parserInput.forget();
                    return name;
                }

                function match(re) {
                    var i = parserInput.i,
                        chunk = parserInput.$re(re);
                    if (chunk) {
                        index.push(i);
                        return name.push(chunk[1]);
                    }
                }

                match(/^(\*?)/);
                while (true) {
                    if (!match(/^((?:[\w-]+)|(?:[@\$]\{[\w-]+\}))/)) {
                        break;
                    }
                }

                if ((name.length > 1) && match(/^((?:\+_|\+)?)\s*:/)) {
                    parserInput.forget();

                    // at last, we have the complete match now. move forward,
                    // convert name particles to tree objects and return:
                    if (name[0] === '') {
                        name.shift();
                        index.shift();
                    }
                    for (k = 0; k < name.length; k++) {
                        s = name[k];
                        name[k] = (s.charAt(0) !== '@' && s.charAt(0) !== '$') ?
                            new(tree.Keyword)(s) :
                            (s.charAt(0) === '@' ?
                                new(tree.Variable)('@' + s.slice(2, -1), index[k], fileInfo) :
                                new(tree.Property)('$' + s.slice(2, -1), index[k], fileInfo));
                    }
                    return name;
                }
                parserInput.restore();
            }
        }
    };
}
function Parser ( context , imports , fileInfo ) { var parsers , parserInput = getParserInput ( ) ; function error ( msg , type ) { throw new LessError ( { index : parserInput . i , filename : fileInfo . filename , type : type || 'Syntax' , message : msg } , imports ) ; } function expect ( arg , msg ) { // some older browsers return typeof 'function' for RegExp var result = ( arg instanceof Function ) ? arg . call ( parsers ) : parserInput . $re ( arg ) ; if ( result ) { return result ; } error ( msg || ( typeof arg === 'string' ? 'expected \'' + arg + '\' got \'' + parserInput . currentChar ( ) + '\'' : 'unexpected token' ) ) ; } // Specialization of expect() function expectChar ( arg , msg ) { if ( parserInput . $char ( arg ) ) { return arg ; } error ( msg || 'expected \'' + arg + '\' got \'' + parserInput . currentChar ( ) + '\'' ) ; } function getDebugInfo ( index ) { var filename = fileInfo . filename ; return { lineNumber : utils . getLocation ( index , parserInput . getInput ( ) ) . line + 1 , fileName : filename } ; } /**
     *  Used after initial parsing to create nodes on the fly
     * 
     *  @param {String} str          - string to parse 
     *  @param {Array}  parseList    - array of parsers to run input through e.g. ["value", "important"]
     *  @param {Number} currentIndex - start number to begin indexing
     *  @param {Object} fileInfo     - fileInfo to attach to created nodes
     */ function parseNode ( str , parseList , currentIndex , fileInfo , callback ) { var result , returnNodes = [ ] ; var parser = parserInput ; try { parser . start ( str , false , function fail ( msg , index ) { callback ( { message : msg , index : index + currentIndex } ) ; } ) ; for ( var x = 0 , p , i ; ( p = parseList [ x ] ) ; x ++ ) { i = parser . i ; result = parsers [ p ] ( ) ; if ( result ) { result . _index = i + currentIndex ; result . _fileInfo = fileInfo ; returnNodes . push ( result ) ; } else { returnNodes . push ( null ) ; } } var endInfo = parser . end ( ) ; if ( endInfo . isFinished ) { callback ( null , returnNodes ) ; } else { callback ( true , null ) ; } } catch ( e ) { throw new LessError ( { index : e . index + currentIndex , message : e . message } , imports , fileInfo . filename ) ; } } // // The Parser // return { parserInput : parserInput , imports : imports , fileInfo : fileInfo , parseNode : parseNode , // // Parse an input string into an abstract syntax tree, // @param str A string containing 'less' markup // @param callback call `callback` when done. // @param [additionalData] An optional map which can contains vars - a map (key, value) of variables to apply // parse : function ( str , callback , additionalData ) { var root , error = null , globalVars , modifyVars , ignored , preText = '' ; globalVars = ( additionalData && additionalData . globalVars ) ? Parser . serializeVars ( additionalData . globalVars ) + '\n' : '' ; modifyVars = ( additionalData && additionalData . modifyVars ) ? '\n' + Parser . serializeVars ( additionalData . modifyVars ) : '' ; if ( context . pluginManager ) { var preProcessors = context . pluginManager . getPreProcessors ( ) ; for ( var i = 0 ; i < preProcessors . length ; i ++ ) { str = preProcessors [ i ] . process ( str , { context : context , imports : imports , fileInfo : fileInfo } ) ; } } if ( globalVars || ( additionalData && additionalData . banner ) ) { preText = ( ( additionalData && additionalData . banner ) ? additionalData . banner : '' ) + globalVars ; ignored = imports . contentsIgnoredChars ; ignored [ fileInfo . filename ] = ignored [ fileInfo . filename ] || 0 ; ignored [ fileInfo . filename ] += preText . length ; } str = str . replace ( / \r\n? / g , '\n' ) ; // Remove potential UTF Byte Order Mark str = preText + str . replace ( / ^\uFEFF / , '' ) + modifyVars ; imports . contents [ fileInfo . filename ] = str ; // Start with the primary rule. // The whole syntax tree is held under a Ruleset node, // with the `root` property set to true, so no `{}` are // output. The callback is called when the input is parsed. try { parserInput . start ( str , context . chunkInput , function fail ( msg , index ) { throw new LessError ( { index : index , type : 'Parse' , message : msg , filename : fileInfo . filename } , imports ) ; } ) ; tree . Node . prototype . parse = this ; root = new tree . Ruleset ( null , this . parsers . primary ( ) ) ; tree . Node . prototype . rootNode = root ; root . root = true ; root . firstRoot = true ; root . functionRegistry = functionRegistry . inherit ( ) ; } catch ( e ) { return callback ( new LessError ( e , imports , fileInfo . filename ) ) ; } // If `i` is smaller than the `input.length - 1`, // it means the parser wasn't able to parse the whole // string, so we've got a parsing error. // // We try to extract a \n delimited string, // showing the line where the parse error occurred. // We split it up into two parts (the part which parsed, // and the part which didn't), so we can color them differently. var endInfo = parserInput . end ( ) ; if ( ! endInfo . isFinished ) { var message = endInfo . furthestPossibleErrorMessage ; if ( ! message ) { message = 'Unrecognised input' ; if ( endInfo . furthestChar === '}' ) { message += '. Possibly missing opening \'{\'' ; } else if ( endInfo . furthestChar === ')' ) { message += '. Possibly missing opening \'(\'' ; } else if ( endInfo . furthestReachedEnd ) { message += '. Possibly missing something' ; } } error = new LessError ( { type : 'Parse' , message : message , index : endInfo . furthest , filename : fileInfo . filename } , imports ) ; } var finish = function ( e ) { e = error || e || imports . error ; if ( e ) { if ( ! ( e instanceof LessError ) ) { e = new LessError ( e , imports , fileInfo . filename ) ; } return callback ( e ) ; } else { return callback ( null , root ) ; } } ; if ( context . processImports !== false ) { new visitors . ImportVisitor ( imports , finish ) . run ( root ) ; } else { return finish ( ) ; } } , // // Here in, the parsing rules/functions // // The basic structure of the syntax tree generated is as follows: // //   Ruleset ->  Declaration -> Value -> Expression -> Entity // // Here's some Less code: // //    .class { //      color: #fff; //      border: 1px solid #000; //      width: @w + 4px; //      > .child {...} //    } // // And here's what the parse tree might look like: // //     Ruleset (Selector '.class', [ //         Declaration ("color",  Value ([Expression [Color #fff]])) //         Declaration ("border", Value ([Expression [Dimension 1px][Keyword "solid"][Color #000]])) //         Declaration ("width",  Value ([Expression [Operation " + " [Variable "@w"][Dimension 4px]]])) //         Ruleset (Selector [Element '>', '.child'], [...]) //     ]) // //  In general, most rules will try to parse a token with the `$re()` function, and if the return //  value is truly, will return a new node, of the relevant type. Sometimes, we need to check //  first, before parsing, that's when we use `peek()`. // parsers : parsers = { // // The `primary` rule is the *entry* and *exit* point of the parser. // The rules here can appear at any level of the parse tree. // // The recursive nature of the grammar is an interplay between the `block` // rule, which represents `{ ... }`, the `ruleset` rule, and this `primary` rule, // as represented by this simplified grammar: // //     primary  →  (ruleset | declaration)+ //     ruleset  →  selector+ block //     block    →  '{' primary '}' // // Only at one point is the primary rule not called from the // block rule: at the root level. // primary : function ( ) { var mixin = this . mixin , root = [ ] , node ; while ( true ) { while ( true ) { node = this . comment ( ) ; if ( ! node ) { break ; } root . push ( node ) ; } // always process comments before deciding if finished if ( parserInput . finished ) { break ; } if ( parserInput . peek ( '}' ) ) { break ; } node = this . extendRule ( ) ; if ( node ) { root = root . concat ( node ) ; continue ; } node = mixin . definition ( ) || this . declaration ( ) || this . ruleset ( ) || mixin . call ( false , false ) || this . variableCall ( ) || this . entities . call ( ) || this . atrule ( ) ; if ( node ) { root . push ( node ) ; } else { var foundSemiColon = false ; while ( parserInput . $char ( ';' ) ) { foundSemiColon = true ; } if ( ! foundSemiColon ) { break ; } } } return root ; } , // comments are collected by the main parsing mechanism and then assigned to nodes // where the current structure allows it comment : function ( ) { if ( parserInput . commentStore . length ) { var comment = parserInput . commentStore . shift ( ) ; return new ( tree . Comment ) ( comment . text , comment . isLineComment , comment . index , fileInfo ) ; } } , // // Entities are tokens which can be found inside an Expression // entities : { mixinLookup : function ( ) { return parsers . mixin . call ( true , true ) ; } , // // A string, which supports escaping " and ' // //     "milky way" 'he\'s the one!' // quoted : function ( forceEscaped ) { var str , index = parserInput . i , isEscaped = false ; parserInput . save ( ) ; if ( parserInput . $char ( '~' ) ) { isEscaped = true ; } else if ( forceEscaped ) { parserInput . restore ( ) ; return ; } str = parserInput . $quoted ( ) ; if ( ! str ) { parserInput . restore ( ) ; return ; } parserInput . forget ( ) ; return new ( tree . Quoted ) ( str . charAt ( 0 ) , str . substr ( 1 , str . length - 2 ) , isEscaped , index , fileInfo ) ; } , // // A catch-all word, such as: // //     black border-collapse // keyword : function ( ) { var k = parserInput . $char ( '%' ) || parserInput . $re ( / ^\[?(?:[\w-]|\\(?:[A-Fa-f0-9]{1,6} ?|[^A-Fa-f0-9]))+\]? / ) ; if ( k ) { return tree . Color . fromKeyword ( k ) || new ( tree . Keyword ) ( k ) ; } } , // // A function call // //     rgb(255, 0, 255) // // The arguments are parsed with the `entities.arguments` parser. // call : function ( ) { var name , args , func , index = parserInput . i ; // http://jsperf.com/case-insensitive-regex-vs-strtolower-then-regex/18 if ( parserInput . peek ( / ^url\( / i ) ) { return ; } parserInput . save ( ) ; name = parserInput . $re ( / ^([\w-]+|%|progid:[\w\.]+)\( / ) ; if ( ! name ) { parserInput . forget ( ) ; return ; } name = name [ 1 ] ; func = this . customFuncCall ( name ) ; if ( func ) { args = func . parse ( ) ; if ( args && func . stop ) { parserInput . forget ( ) ; return args ; } } args = this . arguments ( args ) ; if ( ! parserInput . $char ( ')' ) ) { parserInput . restore ( 'Could not parse call arguments or missing \')\'' ) ; return ; } parserInput . forget ( ) ; return new ( tree . Call ) ( name , args , index , fileInfo ) ; } , // // Parsing rules for functions with non-standard args, e.g.: // //     boolean(not(2 > 1)) // //     This is a quick prototype, to be modified/improved when //     more custom-parsed funcs come (e.g. `selector(...)`) // customFuncCall : function ( name ) { /* Ideally the table is to be moved out of here for faster perf.,
                       but it's quite tricky since it relies on all these `parsers`
                       and `expect` available only here */ return { alpha : f ( parsers . ieAlpha , true ) , boolean : f ( condition ) , 'if' : f ( condition ) } [ name . toLowerCase ( ) ] ; function f ( parse , stop ) { return { parse : parse , // parsing function stop : stop // when true - stop after parse() and return its result,  // otherwise continue for plain args } ; } function condition ( ) { return [ expect ( parsers . condition , 'expected condition' ) ] ; } } , arguments : function ( prevArgs ) { var argsComma = prevArgs || [ ] , argsSemiColon = [ ] , isSemiColonSeparated , value ; parserInput . save ( ) ; while ( true ) { if ( prevArgs ) { prevArgs = false ; } else { value = parsers . detachedRuleset ( ) || this . assignment ( ) || parsers . expression ( ) ; if ( ! value ) { break ; } if ( value . value && value . value . length == 1 ) { value = value . value [ 0 ] ; } argsComma . push ( value ) ; } if ( parserInput . $char ( ',' ) ) { continue ; } if ( parserInput . $char ( ';' ) || isSemiColonSeparated ) { isSemiColonSeparated = true ; value = ( argsComma . length < 1 ) ? argsComma [ 0 ] : new tree . Value ( argsComma ) ; argsSemiColon . push ( value ) ; argsComma = [ ] ; } } parserInput . forget ( ) ; return isSemiColonSeparated ? argsSemiColon : argsComma ; } , literal : function ( ) { return this . dimension ( ) || this . color ( ) || this . quoted ( ) || this . unicodeDescriptor ( ) ; } , // Assignments are argument entities for calls. // They are present in ie filter properties as shown below. // //     filter: progid:DXImageTransform.Microsoft.Alpha( *opacity=50* ) // assignment : function ( ) { var key , value ; parserInput . save ( ) ; key = parserInput . $re ( / ^\w+(?=\s?=) / i ) ; if ( ! key ) { parserInput . restore ( ) ; return ; } if ( ! parserInput . $char ( '=' ) ) { parserInput . restore ( ) ; return ; } value = parsers . entity ( ) ; if ( value ) { parserInput . forget ( ) ; return new ( tree . Assignment ) ( key , value ) ; } else { parserInput . restore ( ) ; } } , // // Parse url() tokens // // We use a specific rule for urls, because they don't really behave like // standard function calls. The difference is that the argument doesn't have // to be enclosed within a string, so it can't be parsed as an Expression. // url : function ( ) { var value , index = parserInput . i ; parserInput . autoCommentAbsorb = false ; if ( ! parserInput . $str ( 'url(' ) ) { parserInput . autoCommentAbsorb = true ; return ; } value = this . quoted ( ) || this . variable ( ) || this . property ( ) || parserInput . $re ( / ^(?:(?:\\[\(\)'"])|[^\(\)'"])+ / ) || '' ; parserInput . autoCommentAbsorb = true ; expectChar ( ')' ) ; return new ( tree . URL ) ( ( value . value != null || value instanceof tree . Variable || value instanceof tree . Property ) ? value : new ( tree . Anonymous ) ( value , index ) , index , fileInfo ) ; } , // // A Variable entity, such as `@fink`, in // //     width: @fink + 2px // // We use a different parser for variable definitions, // see `parsers.variable`. // variable : function ( ) { var ch , name , index = parserInput . i ; parserInput . save ( ) ; if ( parserInput . currentChar ( ) === '@' && ( name = parserInput . $re ( / ^@@?[\w-]+ / ) ) ) { ch = parserInput . currentChar ( ) ; if ( ch === '(' || ch === '[' && ! parserInput . prevChar ( ) . match ( / ^\s / ) ) { // this may be a VariableCall lookup var result = parsers . variableCall ( name ) ; if ( result ) { parserInput . forget ( ) ; return result ; } } parserInput . forget ( ) ; return new ( tree . Variable ) ( name , index , fileInfo ) ; } parserInput . restore ( ) ; } , // A variable entity using the protective {} e.g. @{var} variableCurly : function ( ) { var curly , index = parserInput . i ; if ( parserInput . currentChar ( ) === '@' && ( curly = parserInput . $re ( / ^@\{([\w-]+)\} / ) ) ) { return new ( tree . Variable ) ( '@' + curly [ 1 ] , index , fileInfo ) ; } } , // // A Property accessor, such as `$color`, in // //     background-color: $color // property : function ( ) { var name , index = parserInput . i ; if ( parserInput . currentChar ( ) === '$' && ( name = parserInput . $re ( / ^\$[\w-]+ / ) ) ) { return new ( tree . Property ) ( name , index , fileInfo ) ; } } , // A property entity useing the protective {} e.g. ${prop} propertyCurly : function ( ) { var curly , index = parserInput . i ; if ( parserInput . currentChar ( ) === '$' && ( curly = parserInput . $re ( / ^\$\{([\w-]+)\} / ) ) ) { return new ( tree . Property ) ( '$' + curly [ 1 ] , index , fileInfo ) ; } } , // // A Hexadecimal color // //     #4F3C2F // // `rgb` and `hsl` colors are parsed through the `entities.call` parser. // color : function ( ) { var rgb ; if ( parserInput . currentChar ( ) === '#' && ( rgb = parserInput . $re ( / ^#([A-Fa-f0-9]{8}|[A-Fa-f0-9]{6}|[A-Fa-f0-9]{3,4}) / ) ) ) { return new ( tree . Color ) ( rgb [ 1 ] , undefined , rgb [ 0 ] ) ; } } , colorKeyword : function ( ) { parserInput . save ( ) ; var autoCommentAbsorb = parserInput . autoCommentAbsorb ; parserInput . autoCommentAbsorb = false ; var k = parserInput . $re ( / ^[_A-Za-z-][_A-Za-z0-9-]+ / ) ; parserInput . autoCommentAbsorb = autoCommentAbsorb ; if ( ! k ) { parserInput . forget ( ) ; return ; } parserInput . restore ( ) ; var color = tree . Color . fromKeyword ( k ) ; if ( color ) { parserInput . $str ( k ) ; return color ; } } , // // A Dimension, that is, a number and a unit // //     0.5em 95% // dimension : function ( ) { if ( parserInput . peekNotNumeric ( ) ) { return ; } var value = parserInput . $re ( / ^([+-]?\d*\.?\d+)(%|[a-z_]+)? / i ) ; if ( value ) { return new ( tree . Dimension ) ( value [ 1 ] , value [ 2 ] ) ; } } , // // A unicode descriptor, as is used in unicode-range // // U+0??  or U+00A1-00A9 // unicodeDescriptor : function ( ) { var ud ; ud = parserInput . $re ( / ^U\+[0-9a-fA-F?]+(\-[0-9a-fA-F?]+)? / ) ; if ( ud ) { return new ( tree . UnicodeDescriptor ) ( ud [ 0 ] ) ; } } , // // JavaScript code to be evaluated // //     `window.location.href` // javascript : function ( ) { var js , index = parserInput . i ; parserInput . save ( ) ; var escape = parserInput . $char ( '~' ) ; var jsQuote = parserInput . $char ( '`' ) ; if ( ! jsQuote ) { parserInput . restore ( ) ; return ; } js = parserInput . $re ( / ^[^`]*` / ) ; if ( js ) { parserInput . forget ( ) ; return new ( tree . JavaScript ) ( js . substr ( 0 , js . length - 1 ) , Boolean ( escape ) , index , fileInfo ) ; } parserInput . restore ( 'invalid javascript definition' ) ; } } , // // The variable part of a variable definition. Used in the `rule` parser // //     @fink: // variable : function ( ) { var name ; if ( parserInput . currentChar ( ) === '@' && ( name = parserInput . $re ( / ^(@[\w-]+)\s*: / ) ) ) { return name [ 1 ] ; } } , // // Call a variable value to retrieve a detached ruleset // or a value from a detached ruleset's rules. // //     @fink(); //     @fink; //     color: @fink[@color]; // variableCall : function ( parsedName ) { var lookups , important , i = parserInput . i , inValue = ! ! parsedName , name = parsedName ; parserInput . save ( ) ; if ( name || ( parserInput . currentChar ( ) === '@' && ( name = parserInput . $re ( / ^(@[\w-]+)(\(\s*\))? / ) ) ) ) { lookups = this . mixin . ruleLookups ( ) ; if ( ! lookups && ( ( inValue && parserInput . $str ( '()' ) !== '()' ) || ( name [ 2 ] !== '()' ) ) ) { parserInput . restore ( 'Missing \'[...]\' lookup in variable call' ) ; return ; } if ( ! inValue ) { name = name [ 1 ] ; } if ( lookups && parsers . important ( ) ) { important = true ; } var call = new tree . VariableCall ( name , i , fileInfo ) ; if ( ! inValue && parsers . end ( ) ) { parserInput . forget ( ) ; return call ; } else { parserInput . forget ( ) ; return new tree . NamespaceValue ( call , lookups , important , i , fileInfo ) ; } } parserInput . restore ( ) ; } , // // extend syntax - used to extend selectors // extend : function ( isRule ) { var elements , e , index = parserInput . i , option , extendList , extend ; if ( ! parserInput . $str ( isRule ? '&:extend(' : ':extend(' ) ) { return ; } do { option = null ; elements = null ; while ( ! ( option = parserInput . $re ( / ^(all)(?=\s*(\)|,)) / ) ) ) { e = this . element ( ) ; if ( ! e ) { break ; } if ( elements ) { elements . push ( e ) ; } else { elements = [ e ] ; } } option = option && option [ 1 ] ; if ( ! elements ) { error ( 'Missing target selector for :extend().' ) ; } extend = new ( tree . Extend ) ( new ( tree . Selector ) ( elements ) , option , index , fileInfo ) ; if ( extendList ) { extendList . push ( extend ) ; } else { extendList = [ extend ] ; } } while ( parserInput . $char ( ',' ) ) ; expect ( / ^\) / ) ; if ( isRule ) { expect ( / ^; / ) ; } return extendList ; } , // // extendRule - used in a rule to extend all the parent selectors // extendRule : function ( ) { return this . extend ( true ) ; } , // // Mixins // mixin : { // // A Mixin call, with an optional argument list // //     #mixins > .square(#fff); //     #mixins.square(#fff); //     .rounded(4px, black); //     .button; // // We can lookup / return a value using the lookup syntax: // //     color: #mixin.square(#fff)[@color]; // // The `while` loop is there because mixins can be // namespaced, but we only support the child and descendant // selector for now. // call : function ( inValue , getLookup ) { var s = parserInput . currentChar ( ) , important = false , lookups , index = parserInput . i , elements , args , hasParens ; if ( s !== '.' && s !== '#' ) { return ; } parserInput . save ( ) ; // stop us absorbing part of an invalid selector elements = this . elements ( ) ; if ( elements ) { if ( parserInput . $char ( '(' ) ) { args = this . args ( true ) . args ; expectChar ( ')' ) ; hasParens = true ; } if ( getLookup !== false ) { lookups = this . ruleLookups ( ) ; } if ( getLookup === true && ! lookups ) { parserInput . restore ( ) ; return ; } if ( inValue && ! lookups && ! hasParens ) { // This isn't a valid in-value mixin call parserInput . restore ( ) ; return ; } if ( ! inValue && parsers . important ( ) ) { important = true ; } if ( inValue || parsers . end ( ) ) { parserInput . forget ( ) ; var mixin = new ( tree . mixin . Call ) ( elements , args , index , fileInfo , ! lookups && important ) ; if ( lookups ) { return new tree . NamespaceValue ( mixin , lookups , important ) ; } else { return mixin ; } } } parserInput . restore ( ) ; } , /**
                 * Matching elements for mixins
                 * (Start with . or # and can have > )
                 */ elements : function ( ) { var elements , e , c , elem , elemIndex , re = / ^[#.](?:[\w-]|\\(?:[A-Fa-f0-9]{1,6} ?|[^A-Fa-f0-9]))+ / ; while ( true ) { elemIndex = parserInput . i ; e = parserInput . $re ( re ) ; if ( ! e ) { break ; } elem = new ( tree . Element ) ( c , e , false , elemIndex , fileInfo ) ; if ( elements ) { elements . push ( elem ) ; } else { elements = [ elem ] ; } c = parserInput . $char ( '>' ) ; } return elements ; } , args : function ( isCall ) { var entities = parsers . entities , returner = { args : null , variadic : false } , expressions = [ ] , argsSemiColon = [ ] , argsComma = [ ] , isSemiColonSeparated , expressionContainsNamed , name , nameLoop , value , arg , expand , hasSep = true ; parserInput . save ( ) ; while ( true ) { if ( isCall ) { arg = parsers . detachedRuleset ( ) || parsers . expression ( ) ; } else { parserInput . commentStore . length = 0 ; if ( parserInput . $str ( '...' ) ) { returner . variadic = true ; if ( parserInput . $char ( ';' ) && ! isSemiColonSeparated ) { isSemiColonSeparated = true ; } ( isSemiColonSeparated ? argsSemiColon : argsComma ) . push ( { variadic : true } ) ; break ; } arg = entities . variable ( ) || entities . property ( ) || entities . literal ( ) || entities . keyword ( ) || this . call ( true ) ; } if ( ! arg || ! hasSep ) { break ; } nameLoop = null ; if ( arg . throwAwayComments ) { arg . throwAwayComments ( ) ; } value = arg ; var val = null ; if ( isCall ) { // Variable if ( arg . value && arg . value . length == 1 ) { val = arg . value [ 0 ] ; } } else { val = arg ; } if ( val && ( val instanceof tree . Variable || val instanceof tree . Property ) ) { if ( parserInput . $char ( ':' ) ) { if ( expressions . length > 0 ) { if ( isSemiColonSeparated ) { error ( 'Cannot mix ; and , as delimiter types' ) ; } expressionContainsNamed = true ; } value = parsers . detachedRuleset ( ) || parsers . expression ( ) ; if ( ! value ) { if ( isCall ) { error ( 'could not understand value for named argument' ) ; } else { parserInput . restore ( ) ; returner . args = [ ] ; return returner ; } } nameLoop = ( name = val . name ) ; } else if ( parserInput . $str ( '...' ) ) { if ( ! isCall ) { returner . variadic = true ; if ( parserInput . $char ( ';' ) && ! isSemiColonSeparated ) { isSemiColonSeparated = true ; } ( isSemiColonSeparated ? argsSemiColon : argsComma ) . push ( { name : arg . name , variadic : true } ) ; break ; } else { expand = true ; } } else if ( ! isCall ) { name = nameLoop = val . name ; value = null ; } } if ( value ) { expressions . push ( value ) ; } argsComma . push ( { name : nameLoop , value : value , expand : expand } ) ; if ( parserInput . $char ( ',' ) ) { hasSep = true ; continue ; } hasSep = parserInput . $char ( ';' ) === ';' ; if ( hasSep || isSemiColonSeparated ) { if ( expressionContainsNamed ) { error ( 'Cannot mix ; and , as delimiter types' ) ; } isSemiColonSeparated = true ; if ( expressions . length > 1 ) { value = new ( tree . Value ) ( expressions ) ; } argsSemiColon . push ( { name : name , value : value , expand : expand } ) ; name = null ; expressions = [ ] ; expressionContainsNamed = false ; } } parserInput . forget ( ) ; returner . args = isSemiColonSeparated ? argsSemiColon : argsComma ; return returner ; } , // // A Mixin definition, with a list of parameters // //     .rounded (@radius: 2px, @color) { //        ... //     } // // Until we have a finer grained state-machine, we have to // do a look-ahead, to make sure we don't have a mixin call. // See the `rule` function for more information. // // We start by matching `.rounded (`, and then proceed on to // the argument list, which has optional default values. // We store the parameters in `params`, with a `value` key, // if there is a value, such as in the case of `@radius`. // // Once we've got our params list, and a closing `)`, we parse // the `{...}` block. // definition : function ( ) { var name , params = [ ] , match , ruleset , cond , variadic = false ; if ( ( parserInput . currentChar ( ) !== '.' && parserInput . currentChar ( ) !== '#' ) || parserInput . peek ( / ^[^{]*\} / ) ) { return ; } parserInput . save ( ) ; match = parserInput . $re ( / ^([#.](?:[\w-]|\\(?:[A-Fa-f0-9]{1,6} ?|[^A-Fa-f0-9]))+)\s*\( / ) ; if ( match ) { name = match [ 1 ] ; var argInfo = this . args ( false ) ; params = argInfo . args ; variadic = argInfo . variadic ; // .mixincall("@{a}"); // looks a bit like a mixin definition.. // also // .mixincall(@a: {rule: set;}); // so we have to be nice and restore if ( ! parserInput . $char ( ')' ) ) { parserInput . restore ( 'Missing closing \')\'' ) ; return ; } parserInput . commentStore . length = 0 ; if ( parserInput . $str ( 'when' ) ) { // Guard cond = expect ( parsers . conditions , 'expected condition' ) ; } ruleset = parsers . block ( ) ; if ( ruleset ) { parserInput . forget ( ) ; return new ( tree . mixin . Definition ) ( name , params , ruleset , cond , variadic ) ; } else { parserInput . restore ( ) ; } } else { parserInput . forget ( ) ; } } , ruleLookups : function ( ) { var rule , args , lookups = [ ] ; if ( parserInput . currentChar ( ) !== '[' ) { return ; } while ( true ) { parserInput . save ( ) ; args = null ; rule = this . lookupValue ( ) ; if ( ! rule && rule !== '' ) { parserInput . restore ( ) ; break ; } lookups . push ( rule ) ; parserInput . forget ( ) ; } if ( lookups . length > 0 ) { return lookups ; } } , lookupValue : function ( ) { parserInput . save ( ) ; if ( ! parserInput . $char ( '[' ) ) { parserInput . restore ( ) ; return ; } var name = parserInput . $re ( / ^(?:[@$]{0,2})[_a-zA-Z0-9-]* / ) ; if ( ! parserInput . $char ( ']' ) ) { parserInput . restore ( ) ; return ; } if ( name || name === '' ) { parserInput . forget ( ) ; return name ; } parserInput . restore ( ) ; } } , // // Entities are the smallest recognized token, // and can be found inside a rule's value. // entity : function ( ) { var entities = this . entities ; return this . comment ( ) || entities . literal ( ) || entities . variable ( ) || entities . url ( ) || entities . property ( ) || entities . call ( ) || entities . keyword ( ) || this . mixin . call ( true ) || entities . javascript ( ) ; } , // // A Declaration terminator. Note that we use `peek()` to check for '}', // because the `block` rule will be expecting it, but we still need to make sure // it's there, if ';' was omitted. // end : function ( ) { return parserInput . $char ( ';' ) || parserInput . peek ( '}' ) ; } , // // IE's alpha function // //     alpha(opacity=88) // ieAlpha : function ( ) { var value ; // http://jsperf.com/case-insensitive-regex-vs-strtolower-then-regex/18 if ( ! parserInput . $re ( / ^opacity= / i ) ) { return ; } value = parserInput . $re ( / ^\d+ / ) ; if ( ! value ) { value = expect ( parsers . entities . variable , 'Could not parse alpha' ) ; value = '@{' + value . name . slice ( 1 ) + '}' ; } expectChar ( ')' ) ; return new tree . Quoted ( '' , 'alpha(opacity=' + value + ')' ) ; } , // // A Selector Element // //     div //     + h1 //     #socks //     input[type="text"] // // Elements are the building blocks for Selectors, // they are made out of a `Combinator` (see combinator rule), // and an element name, such as a tag a class, or `*`. // element : function ( ) { var e , c , v , index = parserInput . i ; c = this . combinator ( ) ; e = parserInput . $re ( / ^(?:\d+\.\d+|\d+)% / ) || parserInput . $re ( / ^(?:[.#]?|:*)(?:[\w-]|[^\x00-\x9f]|\\(?:[A-Fa-f0-9]{1,6} ?|[^A-Fa-f0-9]))+ / ) || parserInput . $char ( '*' ) || parserInput . $char ( '&' ) || this . attribute ( ) || parserInput . $re ( / ^\([^&()@]+\) / ) || parserInput . $re ( / ^[\.#:](?=@) / ) || this . entities . variableCurly ( ) ; if ( ! e ) { parserInput . save ( ) ; if ( parserInput . $char ( '(' ) ) { if ( ( v = this . selector ( false ) ) && parserInput . $char ( ')' ) ) { e = new ( tree . Paren ) ( v ) ; parserInput . forget ( ) ; } else { parserInput . restore ( 'Missing closing \')\'' ) ; } } else { parserInput . forget ( ) ; } } if ( e ) { return new ( tree . Element ) ( c , e , e instanceof tree . Variable , index , fileInfo ) ; } } , // // Combinators combine elements together, in a Selector. // // Because our parser isn't white-space sensitive, special care // has to be taken, when parsing the descendant combinator, ` `, // as it's an empty space. We have to check the previous character // in the input, to see if it's a ` ` character. More info on how // we deal with this in *combinator.js*. // combinator : function ( ) { var c = parserInput . currentChar ( ) ; if ( c === '/' ) { parserInput . save ( ) ; var slashedCombinator = parserInput . $re ( / ^\/[a-z]+\/ / i ) ; if ( slashedCombinator ) { parserInput . forget ( ) ; return new ( tree . Combinator ) ( slashedCombinator ) ; } parserInput . restore ( ) ; } if ( c === '>' || c === '+' || c === '~' || c === '|' || c === '^' ) { parserInput . i ++ ; if ( c === '^' && parserInput . currentChar ( ) === '^' ) { c = '^^' ; parserInput . i ++ ; } while ( parserInput . isWhitespace ( ) ) { parserInput . i ++ ; } return new ( tree . Combinator ) ( c ) ; } else if ( parserInput . isWhitespace ( - 1 ) ) { return new ( tree . Combinator ) ( ' ' ) ; } else { return new ( tree . Combinator ) ( null ) ; } } , // // A CSS Selector // with less extensions e.g. the ability to extend and guard // //     .class > div + h1 //     li a:hover // // Selectors are made out of one or more Elements, see above. // selector : function ( isLess ) { var index = parserInput . i , elements , extendList , c , e , allExtends , when , condition ; isLess = isLess !== false ; while ( ( isLess && ( extendList = this . extend ( ) ) ) || ( isLess && ( when = parserInput . $str ( 'when' ) ) ) || ( e = this . element ( ) ) ) { if ( when ) { condition = expect ( this . conditions , 'expected condition' ) ; } else if ( condition ) { error ( 'CSS guard can only be used at the end of selector' ) ; } else if ( extendList ) { if ( allExtends ) { allExtends = allExtends . concat ( extendList ) ; } else { allExtends = extendList ; } } else { if ( allExtends ) { error ( 'Extend can only be used at the end of selector' ) ; } c = parserInput . currentChar ( ) ; if ( elements ) { elements . push ( e ) ; } else { elements = [ e ] ; } e = null ; } if ( c === '{' || c === '}' || c === ';' || c === ',' || c === ')' ) { break ; } } if ( elements ) { return new ( tree . Selector ) ( elements , allExtends , condition , index , fileInfo ) ; } if ( allExtends ) { error ( 'Extend must be used to extend a selector, it cannot be used on its own' ) ; } } , selectors : function ( ) { var s , selectors ; while ( true ) { s = this . selector ( ) ; if ( ! s ) { break ; } if ( selectors ) { selectors . push ( s ) ; } else { selectors = [ s ] ; } parserInput . commentStore . length = 0 ; if ( s . condition && selectors . length > 1 ) { error ( "Guards are only currently allowed on a single selector." ) ; } if ( ! parserInput . $char ( ',' ) ) { break ; } if ( s . condition ) { error ( "Guards are only currently allowed on a single selector." ) ; } parserInput . commentStore . length = 0 ; } return selectors ; } , attribute : function ( ) { if ( ! parserInput . $char ( '[' ) ) { return ; } var entities = this . entities , key , val , op ; if ( ! ( key = entities . variableCurly ( ) ) ) { key = expect ( / ^(?:[_A-Za-z0-9-\*]*\|)?(?:[_A-Za-z0-9-]|\\.)+ / ) ; } op = parserInput . $re ( / ^[|~*$^]?= / ) ; if ( op ) { val = entities . quoted ( ) || parserInput . $re ( / ^[0-9]+% / ) || parserInput . $re ( / ^[\w-]+ / ) || entities . variableCurly ( ) ; } expectChar ( ']' ) ; return new ( tree . Attribute ) ( key , op , val ) ; } , // // The `block` rule is used by `ruleset` and `mixin.definition`. // It's a wrapper around the `primary` rule, with added `{}`. // block : function ( ) { var content ; if ( parserInput . $char ( '{' ) && ( content = this . primary ( ) ) && parserInput . $char ( '}' ) ) { return content ; } } , blockRuleset : function ( ) { var block = this . block ( ) ; if ( block ) { block = new tree . Ruleset ( null , block ) ; } return block ; } , detachedRuleset : function ( ) { var argInfo , params , variadic ; parserInput . save ( ) ; if ( parserInput . $re ( / ^[.#]\( / ) ) { /**
                     * DR args currently only implemented for each() function, and not 
                     * yet settable as `@dr: #(@arg) {}`
                     * This should be done when DRs are merged with mixins.
                     * See: https://github.com/less/less-meta/issues/16
                     */ argInfo = this . mixin . args ( false ) ; params = argInfo . args ; variadic = argInfo . variadic ; if ( ! parserInput . $char ( ')' ) ) { parserInput . restore ( ) ; return ; } } var blockRuleset = this . blockRuleset ( ) ; if ( blockRuleset ) { parserInput . forget ( ) ; if ( params ) { return new tree . mixin . Definition ( null , params , blockRuleset , null , variadic ) ; } return new tree . DetachedRuleset ( blockRuleset ) ; } parserInput . restore ( ) ; } , // // div, .class, body > p {...} // ruleset : function ( ) { var selectors , rules , debugInfo ; parserInput . save ( ) ; if ( context . dumpLineNumbers ) { debugInfo = getDebugInfo ( parserInput . i ) ; } selectors = this . selectors ( ) ; if ( selectors && ( rules = this . block ( ) ) ) { parserInput . forget ( ) ; var ruleset = new ( tree . Ruleset ) ( selectors , rules , context . strictImports ) ; if ( context . dumpLineNumbers ) { ruleset . debugInfo = debugInfo ; } return ruleset ; } else { parserInput . restore ( ) ; } } , declaration : function ( ) { var name , value , index = parserInput . i , hasDR , c = parserInput . currentChar ( ) , important , merge , isVariable ; if ( c === '.' || c === '#' || c === '&' || c === ':' ) { return ; } parserInput . save ( ) ; name = this . variable ( ) || this . ruleProperty ( ) ; if ( name ) { isVariable = typeof name === 'string' ; if ( isVariable ) { value = this . detachedRuleset ( ) ; if ( value ) { hasDR = true ; } } parserInput . commentStore . length = 0 ; if ( ! value ) { // a name returned by this.ruleProperty() is always an array of the form: // [string-1, ..., string-n, ""] or [string-1, ..., string-n, "+"] // where each item is a tree.Keyword or tree.Variable merge = ! isVariable && name . length > 1 && name . pop ( ) . value ; // Custom property values get permissive parsing if ( name [ 0 ] . value && name [ 0 ] . value . slice ( 0 , 2 ) === '--' ) { value = this . permissiveValue ( ) ; } // Try to store values as anonymous // If we need the value later we'll re-parse it in ruleset.parseValue else { value = this . anonymousValue ( ) ; } if ( value ) { parserInput . forget ( ) ; // anonymous values absorb the end ';' which is required for them to work return new ( tree . Declaration ) ( name , value , false , merge , index , fileInfo ) ; } if ( ! value ) { value = this . value ( ) ; } if ( value ) { important = this . important ( ) ; } else if ( isVariable ) { // As a last resort, try permissiveValue value = this . permissiveValue ( ) ; } } if ( value && ( this . end ( ) || hasDR ) ) { parserInput . forget ( ) ; return new ( tree . Declaration ) ( name , value , important , merge , index , fileInfo ) ; } else { parserInput . restore ( ) ; } } else { parserInput . restore ( ) ; } } , anonymousValue : function ( ) { var index = parserInput . i ; var match = parserInput . $re ( / ^([^.#@\$+\/'"*`(;{}-]*); / ) ; if ( match ) { return new ( tree . Anonymous ) ( match [ 1 ] , index ) ; } } , /**
             * Used for custom properties, at-rules, and variables (as fallback)
             * Parses almost anything inside of {} [] () "" blocks
             * until it reaches outer-most tokens.
             * 
             * First, it will try to parse comments and entities to reach
             * the end. This is mostly like the Expression parser except no
             * math is allowed.
             */ permissiveValue : function ( untilTokens ) { var i , e , done , value , tok = untilTokens || ';' , index = parserInput . i , result = [ ] ; function testCurrentChar ( ) { var char = parserInput . currentChar ( ) ; if ( typeof tok === 'string' ) { return char === tok ; } else { return tok . test ( char ) ; } } if ( testCurrentChar ( ) ) { return ; } value = [ ] ; do { e = this . comment ( ) ; if ( e ) { value . push ( e ) ; continue ; } e = this . entity ( ) ; if ( e ) { value . push ( e ) ; } } while ( e ) ; done = testCurrentChar ( ) ; if ( value . length > 0 ) { value = new ( tree . Expression ) ( value ) ; if ( done ) { return value ; } else { result . push ( value ) ; } // Preserve space before $parseUntil as it will not if ( parserInput . prevChar ( ) === ' ' ) { result . push ( new tree . Anonymous ( ' ' , index ) ) ; } } parserInput . save ( ) ; value = parserInput . $parseUntil ( tok ) ; if ( value ) { if ( typeof value === 'string' ) { error ( 'Expected \'' + value + '\'' , 'Parse' ) ; } if ( value . length === 1 && value [ 0 ] === ' ' ) { parserInput . forget ( ) ; return new tree . Anonymous ( '' , index ) ; } var item ; for ( i = 0 ; i < value . length ; i ++ ) { item = value [ i ] ; if ( Array . isArray ( item ) ) { // Treat actual quotes as normal quoted values result . push ( new tree . Quoted ( item [ 0 ] , item [ 1 ] , true , index , fileInfo ) ) ; } else { if ( i === value . length - 1 ) { item = item . trim ( ) ; } // Treat like quoted values, but replace vars like unquoted expressions var quote = new tree . Quoted ( '\'' , item , true , index , fileInfo ) ; quote . variableRegex = / @([\w-]+) / g ; quote . propRegex = / \$([\w-]+) / g ; result . push ( quote ) ; } } parserInput . forget ( ) ; return new tree . Expression ( result , true ) ; } parserInput . restore ( ) ; } , // // An @import atrule // //     @import "lib"; // // Depending on our environment, importing is done differently: // In the browser, it's an XHR request, in Node, it would be a // file-system operation. The function used for importing is // stored in `import`, which we pass to the Import constructor. // 'import' : function ( ) { var path , features , index = parserInput . i ; var dir = parserInput . $re ( / ^@import?\s+ / ) ; if ( dir ) { var options = ( dir ? this . importOptions ( ) : null ) || { } ; if ( ( path = this . entities . quoted ( ) || this . entities . url ( ) ) ) { features = this . mediaFeatures ( ) ; if ( ! parserInput . $char ( ';' ) ) { parserInput . i = index ; error ( 'missing semi-colon or unrecognised media features on import' ) ; } features = features && new ( tree . Value ) ( features ) ; return new ( tree . Import ) ( path , features , options , index , fileInfo ) ; } else { parserInput . i = index ; error ( 'malformed import statement' ) ; } } } , importOptions : function ( ) { var o , options = { } , optionName , value ; // list of options, surrounded by parens if ( ! parserInput . $char ( '(' ) ) { return null ; } do { o = this . importOption ( ) ; if ( o ) { optionName = o ; value = true ; switch ( optionName ) { case 'css' : optionName = 'less' ; value = false ; break ; case 'once' : optionName = 'multiple' ; value = false ; break ; } options [ optionName ] = value ; if ( ! parserInput . $char ( ',' ) ) { break ; } } } while ( o ) ; expectChar ( ')' ) ; return options ; } , importOption : function ( ) { var opt = parserInput . $re ( / ^(less|css|multiple|once|inline|reference|optional) / ) ; if ( opt ) { return opt [ 1 ] ; } } , mediaFeature : function ( ) { var entities = this . entities , nodes = [ ] , e , p ; parserInput . save ( ) ; do { e = entities . keyword ( ) || entities . variable ( ) || entities . mixinLookup ( ) ; if ( e ) { nodes . push ( e ) ; } else if ( parserInput . $char ( '(' ) ) { p = this . property ( ) ; e = this . value ( ) ; if ( parserInput . $char ( ')' ) ) { if ( p && e ) { nodes . push ( new ( tree . Paren ) ( new ( tree . Declaration ) ( p , e , null , null , parserInput . i , fileInfo , true ) ) ) ; } else if ( e ) { nodes . push ( new ( tree . Paren ) ( e ) ) ; } else { error ( 'badly formed media feature definition' ) ; } } else { error ( 'Missing closing \')\'' , 'Parse' ) ; } } } while ( e ) ; parserInput . forget ( ) ; if ( nodes . length > 0 ) { return new ( tree . Expression ) ( nodes ) ; } } , mediaFeatures : function ( ) { var entities = this . entities , features = [ ] , e ; do { e = this . mediaFeature ( ) ; if ( e ) { features . push ( e ) ; if ( ! parserInput . $char ( ',' ) ) { break ; } } else { e = entities . variable ( ) || entities . mixinLookup ( ) ; if ( e ) { features . push ( e ) ; if ( ! parserInput . $char ( ',' ) ) { break ; } } } } while ( e ) ; return features . length > 0 ? features : null ; } , media : function ( ) { var features , rules , media , debugInfo , index = parserInput . i ; if ( context . dumpLineNumbers ) { debugInfo = getDebugInfo ( index ) ; } parserInput . save ( ) ; if ( parserInput . $str ( '@media' ) ) { features = this . mediaFeatures ( ) ; rules = this . block ( ) ; if ( ! rules ) { error ( 'media definitions require block statements after any features' ) ; } parserInput . forget ( ) ; media = new ( tree . Media ) ( rules , features , index , fileInfo ) ; if ( context . dumpLineNumbers ) { media . debugInfo = debugInfo ; } return media ; } parserInput . restore ( ) ; } , // // A @plugin directive, used to import plugins dynamically. // //     @plugin (args) "lib"; // plugin : function ( ) { var path , args , options , index = parserInput . i , dir = parserInput . $re ( / ^@plugin?\s+ / ) ; if ( dir ) { args = this . pluginArgs ( ) ; if ( args ) { options = { pluginArgs : args , isPlugin : true } ; } else { options = { isPlugin : true } ; } if ( ( path = this . entities . quoted ( ) || this . entities . url ( ) ) ) { if ( ! parserInput . $char ( ';' ) ) { parserInput . i = index ; error ( 'missing semi-colon on @plugin' ) ; } return new ( tree . Import ) ( path , null , options , index , fileInfo ) ; } else { parserInput . i = index ; error ( 'malformed @plugin statement' ) ; } } } , pluginArgs : function ( ) { // list of options, surrounded by parens parserInput . save ( ) ; if ( ! parserInput . $char ( '(' ) ) { parserInput . restore ( ) ; return null ; } var args = parserInput . $re ( / ^\s*([^\);]+)\)\s* / ) ; if ( args [ 1 ] ) { parserInput . forget ( ) ; return args [ 1 ] . trim ( ) ; } else { parserInput . restore ( ) ; return null ; } } , // // A CSS AtRule // //     @charset "utf-8"; // atrule : function ( ) { var index = parserInput . i , name , value , rules , nonVendorSpecificName , hasIdentifier , hasExpression , hasUnknown , hasBlock = true , isRooted = true ; if ( parserInput . currentChar ( ) !== '@' ) { return ; } value = this [ 'import' ] ( ) || this . plugin ( ) || this . media ( ) ; if ( value ) { return value ; } parserInput . save ( ) ; name = parserInput . $re ( / ^@[a-z-]+ / ) ; if ( ! name ) { return ; } nonVendorSpecificName = name ; if ( name . charAt ( 1 ) == '-' && name . indexOf ( '-' , 2 ) > 0 ) { nonVendorSpecificName = '@' + name . slice ( name . indexOf ( '-' , 2 ) + 1 ) ; } switch ( nonVendorSpecificName ) { case '@charset' : hasIdentifier = true ; hasBlock = false ; break ; case '@namespace' : hasExpression = true ; hasBlock = false ; break ; case '@keyframes' : case '@counter-style' : hasIdentifier = true ; break ; case '@document' : case '@supports' : hasUnknown = true ; isRooted = false ; break ; default : hasUnknown = true ; break ; } parserInput . commentStore . length = 0 ; if ( hasIdentifier ) { value = this . entity ( ) ; if ( ! value ) { error ( 'expected ' + name + ' identifier' ) ; } } else if ( hasExpression ) { value = this . expression ( ) ; if ( ! value ) { error ( 'expected ' + name + ' expression' ) ; } } else if ( hasUnknown ) { value = this . permissiveValue ( / ^[{;] / ) ; hasBlock = ( parserInput . currentChar ( ) === '{' ) ; if ( ! value ) { if ( ! hasBlock && parserInput . currentChar ( ) !== ';' ) { error ( name + ' rule is missing block or ending semi-colon' ) ; } } else if ( ! value . value ) { value = null ; } } if ( hasBlock ) { rules = this . blockRuleset ( ) ; } if ( rules || ( ! hasBlock && value && parserInput . $char ( ';' ) ) ) { parserInput . forget ( ) ; return new ( tree . AtRule ) ( name , value , rules , index , fileInfo , context . dumpLineNumbers ? getDebugInfo ( index ) : null , isRooted ) ; } parserInput . restore ( 'at-rule options not recognised' ) ; } , // // A Value is a comma-delimited list of Expressions // //     font-family: Baskerville, Georgia, serif; // // In a Rule, a Value represents everything after the `:`, // and before the `;`. // value : function ( ) { var e , expressions = [ ] , index = parserInput . i ; do { e = this . expression ( ) ; if ( e ) { expressions . push ( e ) ; if ( ! parserInput . $char ( ',' ) ) { break ; } } } while ( e ) ; if ( expressions . length > 0 ) { return new ( tree . Value ) ( expressions , index ) ; } } , important : function ( ) { if ( parserInput . currentChar ( ) === '!' ) { return parserInput . $re ( / ^! *important / ) ; } } , sub : function ( ) { var a , e ; parserInput . save ( ) ; if ( parserInput . $char ( '(' ) ) { a = this . addition ( ) ; if ( a && parserInput . $char ( ')' ) ) { parserInput . forget ( ) ; e = new ( tree . Expression ) ( [ a ] ) ; e . parens = true ; return e ; } parserInput . restore ( 'Expected \')\'' ) ; return ; } parserInput . restore ( ) ; } , multiplication : function ( ) { var m , a , op , operation , isSpaced ; m = this . operand ( ) ; if ( m ) { isSpaced = parserInput . isWhitespace ( - 1 ) ; while ( true ) { if ( parserInput . peek ( / ^\/[*\/] / ) ) { break ; } parserInput . save ( ) ; op = parserInput . $char ( '/' ) || parserInput . $char ( '*' ) || parserInput . $str ( './' ) ; if ( ! op ) { parserInput . forget ( ) ; break ; } a = this . operand ( ) ; if ( ! a ) { parserInput . restore ( ) ; break ; } parserInput . forget ( ) ; m . parensInOp = true ; a . parensInOp = true ; operation = new ( tree . Operation ) ( op , [ operation || m , a ] , isSpaced ) ; isSpaced = parserInput . isWhitespace ( - 1 ) ; } return operation || m ; } } , addition : function ( ) { var m , a , op , operation , isSpaced ; m = this . multiplication ( ) ; if ( m ) { isSpaced = parserInput . isWhitespace ( - 1 ) ; while ( true ) { op = parserInput . $re ( / ^[-+]\s+ / ) || ( ! isSpaced && ( parserInput . $char ( '+' ) || parserInput . $char ( '-' ) ) ) ; if ( ! op ) { break ; } a = this . multiplication ( ) ; if ( ! a ) { break ; } m . parensInOp = true ; a . parensInOp = true ; operation = new ( tree . Operation ) ( op , [ operation || m , a ] , isSpaced ) ; isSpaced = parserInput . isWhitespace ( - 1 ) ; } return operation || m ; } } , conditions : function ( ) { var a , b , index = parserInput . i , condition ; a = this . condition ( true ) ; if ( a ) { while ( true ) { if ( ! parserInput . peek ( / ^,\s*(not\s*)?\( / ) || ! parserInput . $char ( ',' ) ) { break ; } b = this . condition ( true ) ; if ( ! b ) { break ; } condition = new ( tree . Condition ) ( 'or' , condition || a , b , index ) ; } return condition || a ; } } , condition : function ( needsParens ) { var result , logical , next ; function or ( ) { return parserInput . $str ( 'or' ) ; } result = this . conditionAnd ( needsParens ) ; if ( ! result ) { return ; } logical = or ( ) ; if ( logical ) { next = this . condition ( needsParens ) ; if ( next ) { result = new ( tree . Condition ) ( logical , result , next ) ; } else { return ; } } return result ; } , conditionAnd : function ( needsParens ) { var result , logical , next , self = this ; function insideCondition ( ) { var cond = self . negatedCondition ( needsParens ) || self . parenthesisCondition ( needsParens ) ; if ( ! cond && ! needsParens ) { return self . atomicCondition ( needsParens ) ; } return cond ; } function and ( ) { return parserInput . $str ( 'and' ) ; } result = insideCondition ( ) ; if ( ! result ) { return ; } logical = and ( ) ; if ( logical ) { next = this . conditionAnd ( needsParens ) ; if ( next ) { result = new ( tree . Condition ) ( logical , result , next ) ; } else { return ; } } return result ; } , negatedCondition : function ( needsParens ) { if ( parserInput . $str ( 'not' ) ) { var result = this . parenthesisCondition ( needsParens ) ; if ( result ) { result . negate = ! result . negate ; } return result ; } } , parenthesisCondition : function ( needsParens ) { function tryConditionFollowedByParenthesis ( me ) { var body ; parserInput . save ( ) ; body = me . condition ( needsParens ) ; if ( ! body ) { parserInput . restore ( ) ; return ; } if ( ! parserInput . $char ( ')' ) ) { parserInput . restore ( ) ; return ; } parserInput . forget ( ) ; return body ; } var body ; parserInput . save ( ) ; if ( ! parserInput . $str ( '(' ) ) { parserInput . restore ( ) ; return ; } body = tryConditionFollowedByParenthesis ( this ) ; if ( body ) { parserInput . forget ( ) ; return body ; } body = this . atomicCondition ( needsParens ) ; if ( ! body ) { parserInput . restore ( ) ; return ; } if ( ! parserInput . $char ( ')' ) ) { parserInput . restore ( 'expected \')\' got \'' + parserInput . currentChar ( ) + '\'' ) ; return ; } parserInput . forget ( ) ; return body ; } , atomicCondition : function ( needsParens ) { var entities = this . entities , index = parserInput . i , a , b , c , op ; function cond ( ) { return this . addition ( ) || entities . keyword ( ) || entities . quoted ( ) || entities . mixinLookup ( ) ; } cond = cond . bind ( this ) ; a = cond ( ) ; if ( a ) { if ( parserInput . $char ( '>' ) ) { if ( parserInput . $char ( '=' ) ) { op = '>=' ; } else { op = '>' ; } } else if ( parserInput . $char ( '<' ) ) { if ( parserInput . $char ( '=' ) ) { op = '<=' ; } else { op = '<' ; } } else if ( parserInput . $char ( '=' ) ) { if ( parserInput . $char ( '>' ) ) { op = '=>' ; } else if ( parserInput . $char ( '<' ) ) { op = '=<' ; } else { op = '=' ; } } if ( op ) { b = cond ( ) ; if ( b ) { c = new ( tree . Condition ) ( op , a , b , index , false ) ; } else { error ( 'expected expression' ) ; } } else { c = new ( tree . Condition ) ( '=' , a , new ( tree . Keyword ) ( 'true' ) , index , false ) ; } return c ; } } , // // An operand is anything that can be part of an operation, // such as a Color, or a Variable // operand : function ( ) { var entities = this . entities , negate ; if ( parserInput . peek ( / ^-[@\$\(] / ) ) { negate = parserInput . $char ( '-' ) ; } var o = this . sub ( ) || entities . dimension ( ) || entities . color ( ) || entities . variable ( ) || entities . property ( ) || entities . call ( ) || entities . quoted ( true ) || entities . colorKeyword ( ) || entities . mixinLookup ( ) ; if ( negate ) { o . parensInOp = true ; o = new ( tree . Negative ) ( o ) ; } return o ; } , // // Expressions either represent mathematical operations, // or white-space delimited Entities. // //     1px solid black //     @var * 2 // expression : function ( ) { var entities = [ ] , e , delim , index = parserInput . i ; do { e = this . comment ( ) ; if ( e ) { entities . push ( e ) ; continue ; } e = this . addition ( ) || this . entity ( ) ; if ( e ) { entities . push ( e ) ; // operations do not allow keyword "/" dimension (e.g. small/20px) so we support that here if ( ! parserInput . peek ( / ^\/[\/*] / ) ) { delim = parserInput . $char ( '/' ) ; if ( delim ) { entities . push ( new ( tree . Anonymous ) ( delim , index ) ) ; } } } } while ( e ) ; if ( entities . length > 0 ) { return new ( tree . Expression ) ( entities ) ; } } , property : function ( ) { var name = parserInput . $re ( / ^(\*?-?[_a-zA-Z0-9-]+)\s*: / ) ; if ( name ) { return name [ 1 ] ; } } , ruleProperty : function ( ) { var name = [ ] , index = [ ] , s , k ; parserInput . save ( ) ; var simpleProperty = parserInput . $re ( / ^([_a-zA-Z0-9-]+)\s*: / ) ; if ( simpleProperty ) { name = [ new ( tree . Keyword ) ( simpleProperty [ 1 ] ) ] ; parserInput . forget ( ) ; return name ; } function match ( re ) { var i = parserInput . i , chunk = parserInput . $re ( re ) ; if ( chunk ) { index . push ( i ) ; return name . push ( chunk [ 1 ] ) ; } } match ( / ^(\*?) / ) ; while ( true ) { if ( ! match ( / ^((?:[\w-]+)|(?:[@\$]\{[\w-]+\})) / ) ) { break ; } } if ( ( name . length > 1 ) && match ( / ^((?:\+_|\+)?)\s*: / ) ) { parserInput . forget ( ) ; // at last, we have the complete match now. move forward, // convert name particles to tree objects and return: if ( name [ 0 ] === '' ) { name . shift ( ) ; index . shift ( ) ; } for ( k = 0 ; k < name . length ; k ++ ) { s = name [ k ] ; name [ k ] = ( s . charAt ( 0 ) !== '@' && s . charAt ( 0 ) !== '$' ) ? new ( tree . Keyword ) ( s ) : ( s . charAt ( 0 ) === '@' ? new ( tree . Variable ) ( '@' + s . slice ( 2 , - 1 ) , index [ k ] , fileInfo ) : new ( tree . Property ) ( '$' + s . slice ( 2 , - 1 ) , index [ k ] , fileInfo ) ) ; } return name ; } parserInput . restore ( ) ; } } } ; }
less.js - parser  A relatively straight-forward predictive parser. There is no tokenization/lexing stage, the input is parsed in one sweep.  To make the parser fast enough to run in the browser, several optimization had to be made:  - Matching and slicing on a huge input is often cause of slowdowns. The solution is to chunkify the input into smaller strings. The chunks are stored in the `chunks` var, `j` holds the current chunk index, and `currentPos` holds the index of the current chunk in relation to `input`. This gives us an almost 4x speed-up.  - In many cases, we don't need to match individual tokens; for example, if a value doesn't hold any variables, operations or dynamic references, the parser can effectively 'skip' it, treating it as a literal. An example would be '1px solid #000' - which evaluates to itself, we don't need to know what the individual components are. The drawback, of course is that you don't get the benefits of syntax-checking on the CSS. This gives us a 50% speed-up in the parser, and a smaller speed-up in the code-gen.   Token matching is done with the `$` function, which either takes a terminal string or regexp, or a non-terminal function to call. It also takes care of moving all the indices forwards.
less . js - parser A relatively straight - forward predictive parser . There is no tokenization / lexing stage the input is parsed in one sweep . To make the parser fast enough to run in the browser several optimization had to be made : - Matching and slicing on a huge input is often cause of slowdowns . The solution is to chunkify the input into smaller strings . The chunks are stored in the chunks var j holds the current chunk index and currentPos holds the index of the current chunk in relation to input . This gives us an almost 4x speed - up . - In many cases we don t need to match individual tokens ; for example if a value doesn t hold any variables operations or dynamic references the parser can effectively skip it treating it as a literal . An example would be 1px solid #000 - which evaluates to itself we don t need to know what the individual components are . The drawback of course is that you don t get the benefits of syntax - checking on the CSS . This gives us a 50% speed - up in the parser and a smaller speed - up in the code - gen . Token matching is done with the $ function which either takes a terminal string or regexp or a non - terminal function to call . It also takes care of moving all the indices forwards .