lib/less/parser/parser.js
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);
                    }
                }
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);
                    }
                }
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 catch-all word, such as:  black border-collapse
A catch - all word such as : black border - collapse