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(...)`)
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')];
                    }
                }