var less, tree;

// Node.js does not have a header file added which defines less if (less === undefined) {

less = exports;
tree = require('./tree');
less.mode = 'node';

} // // 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.Parser = function Parser(env) {

var input,       // LeSS input string
    i,           // current index in `input`
    j,           // current chunk
    saveStack = [],   // holds state for backtracking
    furthest,    // furthest index the parser has gone to
    chunks,      // chunkified input
    current,     // current chunk
    currentPos,  // index of current chunk, in `input`
    parser,
    parsers,
    rootFilename = env && env.filename;

// Top parser on an import tree must be sure there is one "env"
// which will then be passed around by reference.
if (!(env instanceof tree.parseEnv)) {
    env = new tree.parseEnv(env);
}

var imports = this.imports = {
    paths: env.paths || [],  // Search paths, when importing
    queue: [],               // Files which haven't been imported yet
    files: env.files,        // Holds the imported parse trees
    contents: env.contents,  // Holds the imported file contents
    contentsIgnoredChars: env.contentsIgnoredChars, // lines inserted, not in the original less
    mime:  env.mime,         // MIME type of .less files
    error: null,             // Error in parsing/evaluating an import
    push: function (path, currentFileInfo, importOptions, callback) {
        var parserImports = this;
        this.queue.push(path);

        var fileParsedFunc = function (e, root, fullPath) {
            parserImports.queue.splice(parserImports.queue.indexOf(path), 1); // Remove the path from the queue

            var importedPreviously = fullPath === rootFilename;

            parserImports.files[fullPath] = root;                        // Store the root

            if (e && !parserImports.error) { parserImports.error = e; }

            callback(e, root, importedPreviously, fullPath);
        };

        if (less.Parser.importer) {
            less.Parser.importer(path, currentFileInfo, fileParsedFunc, env);
        } else {
            less.Parser.fileLoader(path, currentFileInfo, function(e, contents, fullPath, newFileInfo) {
                if (e) {fileParsedFunc(e); return;}

                var newEnv = new tree.parseEnv(env);

                newEnv.currentFileInfo = newFileInfo;
                newEnv.processImports = false;
                newEnv.contents[fullPath] = contents;

                if (currentFileInfo.reference || importOptions.reference) {
                    newFileInfo.reference = true;
                }

                if (importOptions.inline) {
                    fileParsedFunc(null, contents, fullPath);
                } else {
                    new(less.Parser)(newEnv).parse(contents, function (e, root) {
                        fileParsedFunc(e, root, fullPath);
                    });
                }
            }, env);
        }
    }
};

function save()    { currentPos = i; saveStack.push( { current: current, i: i, j: j }); }
function restore() { var state = saveStack.pop(); current = state.current; currentPos = i = state.i; j = state.j; }
function forget() { saveStack.pop(); }

function sync() {
    if (i > currentPos) {
        current = current.slice(i - currentPos);
        currentPos = i;
    }
}
function isWhitespace(str, pos) {
    var code = str.charCodeAt(pos | 0);
    return (code <= 32) && (code === 32 || code === 10 || code === 9);
}
//
// Parse from a token, regexp or string, and move forward if match
//
function $(tok) {
    var tokType = typeof tok,
        match, length;

    // Either match a single character in the input,
    // or match a regexp in the current chunk (`current`).
    //
    if (tokType === "string") {
        if (input.charAt(i) !== tok) {
            return null;
        }
        skipWhitespace(1);
        return tok;
    }

    // regexp
    sync ();
    if (! (match = tok.exec(current))) {
        return null;
    }

    length = match[0].length;

    // The match is confirmed, add the match length to `i`,
    // and consume any extra white-space characters (' ' || '\n')
    // which come after that. The reason for this is that LeSS's
    // grammar is mostly white-space insensitive.
    //
    skipWhitespace(length);

    if(typeof(match) === 'string') {
        return match;
    } else {
        return match.length === 1 ? match[0] : match;
    }
}

// Specialization of $(tok)
function $re(tok) {
    if (i > currentPos) {
        current = current.slice(i - currentPos);
        currentPos = i;
    }
    var m = tok.exec(current);
    if (!m) {
        return null;
    }

    skipWhitespace(m[0].length);
    if(typeof m === "string") {
        return m;
    }

    return m.length === 1 ? m[0] : m;
}

var _$re = $re;

// Specialization of $(tok)
function $char(tok) {
    if (input.charAt(i) !== tok) {
        return null;
    }
    skipWhitespace(1);
    return tok;
}

function skipWhitespace(length) {
    var oldi = i, oldj = j,
        curr = i - currentPos,
        endIndex = i + current.length - curr,
        mem = (i += length),
        inp = input,
        c;

    for (; i < endIndex; i++) {
        c = inp.charCodeAt(i);
        if (c > 32) {
            break;
        }

        if ((c !== 32) && (c !== 10) && (c !== 9) && (c !== 13)) {
            break;
        }
     }

    current = current.slice(length + i - mem + curr);
    currentPos = i;

    if (!current.length && (j < chunks.length - 1)) {
        current = chunks[++j];
        skipWhitespace(0); // skip space at the beginning of a chunk
        return true; // things changed
    }

    return oldi !== i || oldj !== j;
}

function expect(arg, msg) {
    // some older browsers return typeof 'function' for RegExp
    var result = (Object.prototype.toString.call(arg) === '[object Function]') ? arg.call(parsers) : $(arg);
    if (result) {
        return result;
    }
    error(msg || (typeof(arg) === 'string' ? "expected '" + arg + "' got '" + input.charAt(i) + "'"
                                           : "unexpected token"));
}

// Specialization of expect()
function expectChar(arg, msg) {
    if (input.charAt(i) === arg) {
        skipWhitespace(1);
        return arg;
    }
    error(msg || "expected '" + arg + "' got '" + input.charAt(i) + "'");
}

function error(msg, type) {
    var e = new Error(msg);
    e.index = i;
    e.type = type || 'Syntax';
    throw e;
}

// Same as $(), but don't change the state of the parser,
// just return the match.
function peek(tok) {
    if (typeof(tok) === 'string') {
        return input.charAt(i) === tok;
    } else {
        return tok.test(current);
    }
}

// Specialization of peek()
function peekChar(tok) {
    return input.charAt(i) === tok;
}

function getInput(e, env) {
    if (e.filename && env.currentFileInfo.filename && (e.filename !== env.currentFileInfo.filename)) {
        return parser.imports.contents[e.filename];
    } else {
        return input;
    }
}

function getLocation(index, inputStream) {
    var n = index + 1,
        line = null,
        column = -1;

    while (--n >= 0 && inputStream.charAt(n) !== '\n') {
        column++;
    }

    if (typeof index === 'number') {
        line = (inputStream.slice(0, index).match(/\n/g) || "").length;
    }

    return {
        line: line,
        column: column
    };
}

function getDebugInfo(index, inputStream, env) {
    var filename = env.currentFileInfo.filename;
    if(less.mode !== 'browser' && less.mode !== 'rhino') {
        filename = require('path').resolve(filename);
    }

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

function LessError(e, env) {
    var input = getInput(e, env),
        loc = getLocation(e.index, input),
        line = loc.line,
        col  = loc.column,
        callLine = e.call && getLocation(e.call, input).line,
        lines = input.split('\n');

    this.type = e.type || 'Syntax';
    this.message = e.message;
    this.filename = e.filename || env.currentFileInfo.filename;
    this.index = e.index;
    this.line = typeof(line) === 'number' ? line + 1 : null;
    this.callLine = callLine + 1;
    this.callExtract = lines[callLine];
    this.stack = e.stack;
    this.column = col;
    this.extract = [
        lines[line - 1],
        lines[line],
        lines[line + 1]
    ];
}

LessError.prototype = new Error();
LessError.prototype.constructor = LessError;

this.env = env = env || {};

// The optimization level dictates the thoroughness of the parser,
// the lower the number, the less nodes it will create in the tree.
// This could matter for debugging, or if you want to access
// the individual nodes in the tree.
this.optimization = ('optimization' in this.env) ? this.env.optimization : 1;

//
// The Parser
//
parser = {

    imports: imports,
    //
    // 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, line, lines, error = null, globalVars, modifyVars, preText = "";

        i = j = currentPos = furthest = 0;

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

        if (globalVars || (additionalData && additionalData.banner)) {
            preText = ((additionalData && additionalData.banner) ? additionalData.banner : "") + globalVars;
            parser.imports.contentsIgnoredChars[env.currentFileInfo.filename] = preText.length;
        }

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

        // Split the input into chunks.
        chunks = (function (input) {
            var len = input.length, level = 0, parenLevel = 0,
                lastOpening, lastOpeningParen, lastMultiComment, lastMultiCommentEndBrace,
                chunks = [], emitFrom = 0,
                parserCurrentIndex, currentChunkStartIndex, cc, cc2, matched;

            function fail(msg, index) {
                error = new(LessError)({
                    index: index || parserCurrentIndex,
                    type: 'Parse',
                    message: msg,
                    filename: env.currentFileInfo.filename
                }, env);
            }

            function emitChunk(force) {
                var len = parserCurrentIndex - emitFrom;
                if (((len < 512) && !force) || !len) {
                    return;
                }
                chunks.push(input.slice(emitFrom, parserCurrentIndex + 1));
                emitFrom = parserCurrentIndex + 1;
            }

            for (parserCurrentIndex = 0; parserCurrentIndex < len; parserCurrentIndex++) {
                cc = input.charCodeAt(parserCurrentIndex);
                if (((cc >= 97) && (cc <= 122)) || (cc < 34)) {
                    // a-z or whitespace
                    continue;
                }

                switch (cc) {
                    case 40:                        // (
                        parenLevel++; 
                        lastOpeningParen = parserCurrentIndex; 
                        continue;
                    case 41:                        // )
                        if (--parenLevel < 0) {
                            return fail("missing opening `(`");
                        }
                        continue;
                    case 59:                        // ;
                        if (!parenLevel) { emitChunk(); }
                        continue;
                    case 123:                       // {
                        level++; 
                        lastOpening = parserCurrentIndex; 
                        continue;
                    case 125:                       // }
                        if (--level < 0) {
                            return fail("missing opening `{`");
                        }
                        if (!level && !parenLevel) { emitChunk(); }
                        continue;
                    case 92:                        // \
                        if (parserCurrentIndex < len - 1) { parserCurrentIndex++; continue; }
                        return fail("unescaped `\\`");
                    case 34:
                    case 39:
                    case 96:                        // ", ' and `
                        matched = 0;
                        currentChunkStartIndex = parserCurrentIndex;
                        for (parserCurrentIndex = parserCurrentIndex + 1; parserCurrentIndex < len; parserCurrentIndex++) {
                            cc2 = input.charCodeAt(parserCurrentIndex);
                            if (cc2 > 96) { continue; }
                            if (cc2 == cc) { matched = 1; break; }
                            if (cc2 == 92) {        // \
                                if (parserCurrentIndex == len - 1) {
                                    return fail("unescaped `\\`");
                                }
                                parserCurrentIndex++;
                            }
                        }
                        if (matched) { continue; }
                        return fail("unmatched `" + String.fromCharCode(cc) + "`", currentChunkStartIndex);
                    case 47:                        // /, check for comment
                        if (parenLevel || (parserCurrentIndex == len - 1)) { continue; }
                        cc2 = input.charCodeAt(parserCurrentIndex + 1);
                        if (cc2 == 47) {
                            // //, find lnfeed
                            for (parserCurrentIndex = parserCurrentIndex + 2; parserCurrentIndex < len; parserCurrentIndex++) {
                                cc2 = input.charCodeAt(parserCurrentIndex);
                                if ((cc2 <= 13) && ((cc2 == 10) || (cc2 == 13))) { break; }
                            }
                        } else if (cc2 == 42) {
                            // /*, find */
                            lastMultiComment = currentChunkStartIndex = parserCurrentIndex;
                            for (parserCurrentIndex = parserCurrentIndex + 2; parserCurrentIndex < len - 1; parserCurrentIndex++) {
                                cc2 = input.charCodeAt(parserCurrentIndex);
                                if (cc2 == 125) { lastMultiCommentEndBrace = parserCurrentIndex; }
                                if (cc2 != 42) { continue; }
                                if (input.charCodeAt(parserCurrentIndex + 1) == 47) { break; }
                            }
                            if (parserCurrentIndex == len - 1) {
                                return fail("missing closing `*/`", currentChunkStartIndex);
                            }
                            parserCurrentIndex++;
                        }
                        continue;
                    case 42:                       // *, check for unmatched */
                        if ((parserCurrentIndex < len - 1) && (input.charCodeAt(parserCurrentIndex + 1) == 47)) {
                            return fail("unmatched `/*`");
                        }
                        continue;
                }
            }

            if (level !== 0) {
                if ((lastMultiComment > lastOpening) && (lastMultiCommentEndBrace > lastMultiComment)) {
                    return fail("missing closing `}` or `*/`", lastOpening);
                } else {
                    return fail("missing closing `}`", lastOpening);
                }
            } else if (parenLevel !== 0) {
                return fail("missing closing `)`", lastOpeningParen);
            }

            emitChunk(true);
            return chunks;
        })(str);

        if (error) {
            return callback(new(LessError)(error, env));
        }

        current = chunks[0];

        // 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 {
            root = new(tree.Ruleset)(null, this.parsers.primary());
            root.root = true;
            root.firstRoot = true;
        } catch (e) {
            return callback(new(LessError)(e, env));
        }

        root.toCSS = (function (evaluate) {
            return function (options, variables) {
                options = options || {};
                var evaldRoot,
                    css,
                    evalEnv = new tree.evalEnv(options);

                //
                // Allows setting variables with a hash, so:
                //
                //   `{ color: new(tree.Color)('#f01') }` will become:
                //
                //   new(tree.Rule)('@color',
                //     new(tree.Value)([
                //       new(tree.Expression)([
                //         new(tree.Color)('#f01')
                //       ])
                //     ])
                //   )
                //
                if (typeof(variables) === 'object' && !Array.isArray(variables)) {
                    variables = Object.keys(variables).map(function (k) {
                        var value = variables[k];

                        if (! (value instanceof tree.Value)) {
                            if (! (value instanceof tree.Expression)) {
                                value = new(tree.Expression)([value]);
                            }
                            value = new(tree.Value)([value]);
                        }
                        return new(tree.Rule)('@' + k, value, false, null, 0);
                    });
                    evalEnv.frames = [new(tree.Ruleset)(null, variables)];
                }

                try {
                    var preEvalVisitors = [],
                        visitors = [
                            new(tree.joinSelectorVisitor)(),
                            new(tree.processExtendsVisitor)(),
                            new(tree.toCSSVisitor)({compress: Boolean(options.compress)})
                        ], i, root = this;

                    if (options.plugins) {
                        for(i =0; i < options.plugins.length; i++) {
                            if (options.plugins[i].isPreEvalVisitor) {
                                preEvalVisitors.push(options.plugins[i]);
                            } else {
                                if (options.plugins[i].isPreVisitor) {
                                    visitors.splice(0, 0, options.plugins[i]);
                                } else {
                                    visitors.push(options.plugins[i]);
                                }
                            }
                        }
                    }

                    for(i = 0; i < preEvalVisitors.length; i++) {
                        preEvalVisitors[i].run(root);
                    }

                    evaldRoot = evaluate.call(root, evalEnv);

                    for(i = 0; i < visitors.length; i++) {
                        visitors[i].run(evaldRoot);
                    }

                    if (options.sourceMap) {
                        evaldRoot = new tree.sourceMapOutput(
                            {
                                contentsIgnoredCharsMap: parser.imports.contentsIgnoredChars,
                                writeSourceMap: options.writeSourceMap,
                                rootNode: evaldRoot,
                                contentsMap: parser.imports.contents,
                                sourceMapFilename: options.sourceMapFilename,
                                sourceMapURL: options.sourceMapURL,
                                outputFilename: options.sourceMapOutputFilename,
                                sourceMapBasepath: options.sourceMapBasepath,
                                sourceMapRootpath: options.sourceMapRootpath,
                                outputSourceFiles: options.outputSourceFiles,
                                sourceMapGenerator: options.sourceMapGenerator
                            });
                    }

                    css = evaldRoot.toCSS({
                            compress: Boolean(options.compress),
                            dumpLineNumbers: env.dumpLineNumbers,
                            strictUnits: Boolean(options.strictUnits),
                            numPrecision: 8});
                } catch (e) {
                    throw new(LessError)(e, env);
                }

                if (options.cleancss && less.mode === 'node') {
                    var CleanCSS = require('clean-css'),
                        cleancssOptions = options.cleancssOptions || {};

                    if (cleancssOptions.keepSpecialComments === undefined) {
                        cleancssOptions.keepSpecialComments = "*";
                    }
                    cleancssOptions.processImport = false;
                    cleancssOptions.noRebase = true;
                    if (cleancssOptions.noAdvanced === undefined) {
                        cleancssOptions.noAdvanced = true;
                    }

                    return new CleanCSS(cleancssOptions).minify(css);
                } else if (options.compress) {
                    return css.replace(/(^(\s)+)|((\s)+$)/g, "");
                } else {
                    return css;
                }
            };
        })(root.eval);

        // 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 occured.
        // We split it up into two parts (the part which parsed,
        // and the part which didn't), so we can color them differently.
        if (i < input.length - 1) {
            i = furthest;
            var loc = getLocation(i, input);
            lines = input.split('\n');
            line = loc.line + 1;

            error = {
                type: "Parse",
                message: "Unrecognised input",
                index: i,
                filename: env.currentFileInfo.filename,
                line: line,
                column: loc.column,
                extract: [
                    lines[line - 2],
                    lines[line - 1],
                    lines[line]
                ]
            };
        }

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

            if (e) {
                if (!(e instanceof LessError)) {
                    e = new(LessError)(e, env);
                }

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

        if (env.processImports !== false) {
            new tree.importVisitor(this.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 ->  Rule -> 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', [
    //         Rule ("color",  Value ([Expression [Color #fff]]))
    //         Rule ("border", Value ([Expression [Dimension 1px][Keyword "solid"][Color #000]]))
    //         Rule ("width",  Value ([Expression [Operation "+" [Variable "@w"][Dimension 4px]]]))
    //         Ruleset (Selector [Element '>', '.child'], [...])
    //     ])
    //
    //  In general, most rules will try to parse a token with the `$()` 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 | rule)+
        //     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, $re = _$re, root = [], node;

            while (current)
            {
                node = this.extendRule() || mixin.definition() || this.rule() || this.ruleset() ||
                    mixin.call() || this.comment() || this.rulesetCall() || this.directive();
                if (node) {
                    root.push(node);
                } else {
                    if (!($re(/^[\s\n]+/) || $re(/^;+/))) {
                        break;
                    }
                }
                if (peekChar('}')) {
                    break;
                }
            }

            return root;
        },

        // We create a Comment node for CSS comments `/* */`,
        // but keep the LeSS comments `//` silent, by just skipping
        // over them.
        comment: function () {
            var comment;

            if (input.charAt(i) !== '/') { return; }

            if (input.charAt(i + 1) === '/') {
                return new(tree.Comment)($re(/^\/\/.*/), true, i, env.currentFileInfo);
            }
            comment = $re(/^\/\*(?:[^*]|\*+[^\/*])*\*+\/\n?/);
            if (comment) {
                return new(tree.Comment)(comment, false, i, env.currentFileInfo);
            }
        },

        comments: function () {
            var comment, comments = [];

            while(true) {
                comment = this.comment();
                if (!comment) {
                    break;
                }
                comments.push(comment);
            }

            return comments;
        },

        //
        // Entities are tokens which can be found inside an Expression
        //
        entities: {
            //
            // A string, which supports escaping " and '
            //
            //     "milky way" 'he\'s the one!'
            //
            quoted: function () {
                var str, j = i, e, index = i;

                if (input.charAt(j) === '~') { j++; e = true; } // Escaped strings
                if (input.charAt(j) !== '"' && input.charAt(j) !== "'") { return; }

                if (e) { $char('~'); }

                str = $re(/^"((?:[^"\\\r\n]|\\.)*)"|'((?:[^'\\\r\n]|\\.)*)'/);
                if (str) {
                    return new(tree.Quoted)(str[0], str[1] || str[2], e, index, env.currentFileInfo);
                }
            },

            //
            // A catch-all word, such as:
            //
            //     black border-collapse
            //
            keyword: function () {
                var k;

                k = $re(/^%|^[_A-Za-z-][_A-Za-z0-9-]*/);
                if (k) {
                    var color = tree.Color.fromKeyword(k);
                    if (color) {
                        return color;
                    }
                    return new(tree.Keyword)(k);
                }
            },

            //
            // A function call
            //
            //     rgb(255, 0, 255)
            //
            // We also try to catch IE's `alpha()`, but let the `alpha` parser
            // deal with the details.
            //
            // The arguments are parsed with the `entities.arguments` parser.
            //
            call: function () {
                var name, nameLC, args, alpha_ret, index = i;

                name = /^([\w-]+|%|progid:[\w\.]+)\(/.exec(current);
                if (!name) { return; }

                name = name[1];
                nameLC = name.toLowerCase();
                if (nameLC === 'url') {
                    return null;
                }

                i += name.length;

                if (nameLC === 'alpha') {
                    alpha_ret = parsers.alpha();
                    if(typeof alpha_ret !== 'undefined') {
                        return alpha_ret;
                    }
                }

                $char('('); // Parse the '(' and consume whitespace.

                args = this.arguments();

                if (! $char(')')) {
                    return;
                }

                if (name) { return new(tree.Call)(name, args, index, env.currentFileInfo); }
            },
            arguments: function () {
                var args = [], arg;

                while (true) {
                    arg = this.assignment() || parsers.expression();
                    if (!arg) {
                        break;
                    }
                    args.push(arg);
                    if (! $char(',')) {
                        break;
                    }
                }
                return args;
            },
            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;
                key = $re(/^\w+(?=\s?=)/i);
                if (!key) {
                    return;
                }
                if (!$char('=')) {
                    return;
                }
                value = parsers.entity();
                if (value) {
                    return new(tree.Assignment)(key, value);
                }
            },

            //
            // 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;

                if (input.charAt(i) !== 'u' || !$re(/^url\(/)) {
                    return;
                }

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

                expectChar(')');

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

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

                if (input.charAt(i) === '@' && (name = $re(/^@@?[\w-]+/))) {
                    return new(tree.Variable)(name, index, env.currentFileInfo);
                }
            },

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

                if (input.charAt(i) === '@' && (curly = $re(/^@\{([\w-]+)\}/))) {
                    return new(tree.Variable)("@" + curly[1], index, env.currentFileInfo);
                }
            },

            //
            // A Hexadecimal color
            //
            //     #4F3C2F
            //
            // `rgb` and `hsl` colors are parsed through the `entities.call` parser.
            //
            color: function () {
                var rgb;

                if (input.charAt(i) === '#' && (rgb = $re(/^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})/))) {
                    return new(tree.Color)(rgb[1]);
                }
            },

            //
            // A Dimension, that is, a number and a unit
            //
            //     0.5em 95%
            //
            dimension: function () {
                var value, c = input.charCodeAt(i);
                //Is the first char of the dimension 0-9, '.', '+' or '-'
                if ((c > 57 || c < 43) || c === 47 || c == 44) {
                    return;
                }

                value = $re(/^([+-]?\d*\.?\d+)(%|[a-z]+)?/);
                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 = $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 str, j = i, e;

                if (input.charAt(j) === '~') { j++; e = true; } // Escaped strings
                if (input.charAt(j) !== '`') { return; }
                if (env.javascriptEnabled !== undefined && !env.javascriptEnabled) {
                    error("You are using JavaScript, which has been disabled.");
                }

                if (e) { $char('~'); }

                str = $re(/^`([^`]*)`/);
                if (str) {
                    return new(tree.JavaScript)(str[1], i, e);
                }
            }
        },

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

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

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

            if (input.charAt(i) === '@' && (name = $re(/^(@[\w-]+)\s*\(\s*\)\s*;/))) { 
                return new tree.RulesetCall(name[1]); 
            }
        },

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

            if (!(isRule ? $re(/^&:extend\(/) : $re(/^:extend\(/))) { return; }

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

                option = option && option[1];

                extend = new(tree.Extend)(new(tree.Selector)(elements), option, index);
                if (extendList) { extendList.push(extend); } else { extendList = [ extend ]; }

            } while($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);
            //     .rounded(4px, black);
            //     .button;
            //
            // The `while` loop is there because mixins can be
            // namespaced, but we only support the child and descendant
            // selector for now.
            //
            call: function () {
                var s = input.charAt(i), important = false, index = i, elemIndex,
                    elements, elem, e, c, args;

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

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

                while (true) {
                    elemIndex = i;
                    e = $re(/^[#.](?:[\w-]|\\(?:[A-Fa-f0-9]{1,6} ?|[^A-Fa-f0-9]))+/);
                    if (!e) {
                        break;
                    }
                    elem = new(tree.Element)(c, e, elemIndex, env.currentFileInfo);
                    if (elements) { elements.push(elem); } else { elements = [ elem ]; }
                    c = $char('>');
                }

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

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

                    if (parsers.end()) {
                        forget();
                        return new(tree.mixin.Call)(elements, args, index, env.currentFileInfo, important);
                    }
                }

                restore();
            },
            args: function (isCall) {
                var parsers = parser.parsers, entities = parsers.entities,
                    returner = { args:null, variadic: false },
                    expressions = [], argsSemiColon = [], argsComma = [],
                    isSemiColonSeperated, expressionContainsNamed, name, nameLoop, value, arg;

                save();

                while (true) {
                    if (isCall) {
                        arg = parsers.detachedRuleset() || parsers.expression();
                    } else {
                        parsers.comments();
                        if (input.charAt(i) === '.' && $re(/^\.{3}/)) {
                            returner.variadic = true;
                            if ($char(";") && !isSemiColonSeperated) {
                                isSemiColonSeperated = true;
                            }
                            (isSemiColonSeperated ? argsSemiColon : argsComma)
                                .push({ variadic: true });
                            break;
                        }
                        arg = entities.variable() || entities.literal() || entities.keyword();
                    }

                    if (!arg) {
                        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) {
                        if ($char(':')) {
                            if (expressions.length > 0) {
                                if (isSemiColonSeperated) {
                                    error("Cannot mix ; and , as delimiter types");
                                }
                                expressionContainsNamed = true;
                            }

                            // we do not support setting a ruleset as a default variable - it doesn't make sense
                            // However if we do want to add it, there is nothing blocking it, just don't error
                            // and remove isCall dependency below
                            value = (isCall && parsers.detachedRuleset()) || parsers.expression();

                            if (!value) {
                                if (isCall) {
                                    error("could not understand value for named argument");
                                } else {
                                    restore();
                                    returner.args = [];
                                    return returner;
                                }
                            }
                            nameLoop = (name = val.name);
                        } else if (!isCall && $re(/^\.{3}/)) {
                            returner.variadic = true;
                            if ($char(";") && !isSemiColonSeperated) {
                                isSemiColonSeperated = true;
                            }
                            (isSemiColonSeperated ? argsSemiColon : argsComma)
                                .push({ name: arg.name, variadic: true });
                            break;
                        } else if (!isCall) {
                            name = nameLoop = val.name;
                            value = null;
                        }
                    }

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

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

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

                    if ($char(';') || isSemiColonSeperated) {

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

                        isSemiColonSeperated = true;

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

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

                forget();
                returner.args = isSemiColonSeperated ? 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 ((input.charAt(i) !== '.' && input.charAt(i) !== '#') ||
                    peek(/^[^{]*\}/)) {
                    return;
                }

                save();

                match = $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 (!$char(')')) {
                        furthest = i;
                        restore();
                        return;
                    }

                    parsers.comments();

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

                    ruleset = parsers.block();

                    if (ruleset) {
                        forget();
                        return new(tree.mixin.Definition)(name, params, ruleset, cond, variadic);
                    } else {
                        restore();
                    }
                } else {
                    forget();
                }
            }
        },

        //
        // Entities are the smallest recognized token,
        // and can be found inside a rule's value.
        //
        entity: function () {
            var entities = this.entities;

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

        //
        // A Rule 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 ommitted.
        //
        end: function () {
            return $char(';') || peekChar('}');
        },

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

            if (! $re(/^\(opacity=/i)) { return; }
            value = $re(/^\d+/) || this.entities.variable();
            if (value) {
                expectChar(')');
                return new(tree.Alpha)(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 = i;

            c = this.combinator();

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

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

            if (e) { return new(tree.Element)(c, e, index, env.currentFileInfo); }
        },

        //
        // 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 = input.charAt(i);

            if (c === '>' || c === '+' || c === '~' || c === '|' || c === '^') {
                i++;
                if (input.charAt(i) === '^') {
                    c = '^^';
                    i++;
                }
                while (isWhitespace(input, i)) { i++; }
                return new(tree.Combinator)(c);
            } else if (isWhitespace(input, i - 1)) {
                return new(tree.Combinator)(" ");
            } else {
                return new(tree.Combinator)(null);
            }
        },
        //
        // A CSS selector (see selector below)
        // with less extensions e.g. the ability to extend and guard
        //
        lessSelector: function () {
            return this.selector(true);
        },
        //
        // A CSS Selector
        //
        //     .class > div + h1
        //     li a:hover
        //
        // Selectors are made out of one or more Elements, see above.
        //
        selector: function (isLess) {
            var index = i, $re = _$re, elements, extendList, c, e, extend, when, condition;

            while ((isLess && (extend = this.extend())) || (isLess && (when = $re(/^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 (extend) {
                    if (extendList) { extendList.push(extend); } else { extendList = [ extend ]; }
                } else {
                    if (extendList) { error("Extend can only be used at the end of selector"); }
                    c = input.charAt(i);
                    if (elements) { elements.push(e); } else { elements = [ e ]; }
                    e = null;
                }
                if (c === '{' || c === '}' || c === ';' || c === ',' || c === ')') {
                    break;
                }
            }

            if (elements) { return new(tree.Selector)(elements, extendList, condition, index, env.currentFileInfo); }
            if (extendList) { error("Extend must be used to extend a selector, it cannot be used on its own"); }
        },
        attribute: function () {
            if (! $char('[')) { return; }

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

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

            op = $re(/^[|~*$^]?=/);
            if (op) {
                val = entities.quoted() || $re(/^[0-9]+%/) || $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 ($char('{') && (content = this.primary()) && $char('}')) {
                return content;
            }
        },

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

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

        detachedRuleset: function() {
            var blockRuleset = this.blockRuleset();
            if (blockRuleset) {
                return new tree.DetachedRuleset(blockRuleset);
            }
        },

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

            save();

            if (env.dumpLineNumbers) {
                debugInfo = getDebugInfo(i, input, env);
            }

            while (true) {
                s = this.lessSelector();
                if (!s) {
                    break;
                }
                if (selectors) { selectors.push(s); } else { selectors = [ s ]; }
                this.comments();
                if (s.condition && selectors.length > 1) {
                    error("Guards are only currently allowed on a single selector.");
                }
                if (! $char(',')) { break; }
                if (s.condition) {
                    error("Guards are only currently allowed on a single selector.");
                }
                this.comments();
            }

            if (selectors && (rules = this.block())) {
                forget();
                var ruleset = new(tree.Ruleset)(selectors, rules, env.strictImports);
                if (env.dumpLineNumbers) {
                    ruleset.debugInfo = debugInfo;
                }
                return ruleset;
            } else {
                // Backtrack
                furthest = i;
                restore();
            }
        },
        rule: function (tryAnonymous) {
            var name, value, startOfRule = i, c = input.charAt(startOfRule), important, merge, isVariable;

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

            save();

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

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

                if (!value) {
                    // prefer to try to parse first if its a variable or we are compressing
                    // but always fallback on the other one
                    value = !tryAnonymous && (env.compress || isVariable) ?
                        (this.value() || this.anonymousValue()) :
                        (this.anonymousValue() || this.value());

                    important = this.important();

                    // 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.pop().value;
                }

                if (value && this.end()) {
                    forget();
                    return new (tree.Rule)(name, value, important, merge, startOfRule, env.currentFileInfo);
                } else {
                    furthest = i;
                    restore();
                    if (value && !tryAnonymous) {
                        return this.rule(true);
                    }
                }
            } else {
                forget();
            }
        },
        anonymousValue: function () {
            var match;
            match = /^([^@+\/'"*`(;{}-]*);/.exec(current);
            if (match) {
                i += match[0].length - 1;
                return new(tree.Anonymous)(match[1]);
            }
        },

        //
        // An @import directive
        //
        //     @import "lib";
        //
        // Depending on our environemnt, 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 = i;

            save();

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

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

            if (dir && (path = this.entities.quoted() || this.entities.url())) {
                features = this.mediaFeatures();
                if ($char(';')) {
                    forget();
                    features = features && new(tree.Value)(features);
                    return new(tree.Import)(path, features, options, index, env.currentFileInfo);
                }
            }

            restore();
        },

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

            // list of options, surrounded by parens
            if (! $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 (! $char(',')) { break; }
                }
            } while (o);
            expectChar(')');
            return options;
        },

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

        mediaFeature: function () {
            var entities = this.entities, nodes = [], e, p;
            do {
                e = entities.keyword() || entities.variable();
                if (e) {
                    nodes.push(e);
                } else if ($char('(')) {
                    p = this.property();
                    e = this.value();
                    if ($char(')')) {
                        if (p && e) {
                            nodes.push(new(tree.Paren)(new(tree.Rule)(p, e, null, null, i, env.currentFileInfo, true)));
                        } else if (e) {
                            nodes.push(new(tree.Paren)(e));
                        } else {
                            return null;
                        }
                    } else { return null; }
                }
            } while (e);

            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 (! $char(',')) { break; }
                } else {
                    e = entities.variable();
                    if (e) {
                        features.push(e);
                        if (! $char(',')) { break; }
                    }
                }
            } while (e);

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

        media: function () {
            var features, rules, media, debugInfo;

            if (env.dumpLineNumbers) {
                debugInfo = getDebugInfo(i, input, env);
            }

            if ($re(/^@media/)) {
                features = this.mediaFeatures();

                rules = this.block();
                if (rules) {
                    media = new(tree.Media)(rules, features, i, env.currentFileInfo);
                    if (env.dumpLineNumbers) {
                        media.debugInfo = debugInfo;
                    }
                    return media;
                }
            }
        },

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

            if (input.charAt(i) !== '@') { return; }

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

            save();

            name = $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 "@font-face":
                case "@viewport":
                case "@top-left":
                case "@top-left-corner":
                case "@top-center":
                case "@top-right":
                case "@top-right-corner":
                case "@bottom-left":
                case "@bottom-left-corner":
                case "@bottom-center":
                case "@bottom-right":
                case "@bottom-right-corner":
                case "@left-top":
                case "@left-middle":
                case "@left-bottom":
                case "@right-top":
                case "@right-middle":
                case "@right-bottom":
                    hasBlock = true;
                    break;
                */
                case "@charset":
                    hasIdentifier = true;
                    hasBlock = false;
                    break;
                case "@namespace":
                    hasExpression = true;
                    hasBlock = false;
                    break;
                case "@keyframes":
                    hasIdentifier = true;
                    break;
                case "@host":
                case "@page":
                case "@document":
                case "@supports":
                    hasUnknown = true;
                    break;
            }

            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 = ($re(/^[^{;]+/) || '').trim();
                if (value) {
                    value = new(tree.Anonymous)(value);
                }
            }

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

            if (rules || (!hasBlock && value && $char(';'))) {
                forget();
                return new(tree.Directive)(name, value, rules, index, env.currentFileInfo, 
                    env.dumpLineNumbers ? getDebugInfo(index, input, env) : null);
            }

            restore();
        },

        //
        // 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 = [];

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

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

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

                    if (!op) { break; }

                    a = this.operand();

                    if (!a) { break; }

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

            a = this.condition();
            if (a) {
                while (true) {
                    if (!peek(/^,\s*(not\s*)?\(/) || !$char(',')) {
                        break;
                    }
                    b = this.condition();
                    if (!b) {
                        break;
                    }
                    condition = new(tree.Condition)('or', condition || a, b, index);
                }
                return condition || a;
            }
        },
        condition: function () {
            var entities = this.entities, index = i, negate = false,
                a, b, c, op;

            if ($re(/^not/)) { negate = true; }
            expectChar('(');
            a = this.addition() || entities.keyword() || entities.quoted();
            if (a) {
                op = $re(/^(?:>=|<=|=<|[<=>])/);
                if (op) {
                    b = this.addition() || entities.keyword() || entities.quoted();
                    if (b) {
                        c = new(tree.Condition)(op, a, b, index, negate);
                    } else {
                        error('expected expression');
                    }
                } else {
                    c = new(tree.Condition)('=', a, new(tree.Keyword)('true'), index, negate);
                }
                expectChar(')');
                return $re(/^and/) ? new(tree.Condition)('and', c, this.condition()) : 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,
                p = input.charAt(i + 1), negate;

            if (input.charAt(i) === '-' && (p === '@' || p === '(')) { negate = $char('-'); }
            var o = this.sub() || entities.dimension() ||
                    entities.color() || entities.variable() ||
                    entities.call();

            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;

            do {
                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 (!peek(/^\/[\/*]/)) {
                        delim = $char('/');
                        if (delim) {
                            entities.push(new(tree.Anonymous)(delim));
                        }
                    }
                }
            } while (e);
            if (entities.length > 0) {
                return new(tree.Expression)(entities);
            }
        },
        property: function () {
            var name = $re(/^(\*?-?[_a-zA-Z0-9-]+)\s*:/);
            if (name) {
                return name[1];
            }
        },
        ruleProperty: function () {
            var c = current, name = [], index = [], length = 0, s, k;

            function match(re) {
                var a = re.exec(c);
                if (a) {
                    index.push(i + length);
                    length += a[0].length;
                    c = c.slice(a[1].length);
                    return name.push(a[1]);
                }
            }

            match(/^(\*?)/);
            while (match(/^((?:[\w-]+)|(?:@\{[\w-]+\}))/)); // !
            if ((name.length > 1) && match(/^\s*((?:\+_|\+)?)\s*:/)) {
                // at last, we have the complete match now. move forward, 
                // convert name particles to tree objects and return:
                skipWhitespace(length);
                if (name[0] === '') {
                    name.shift();
                    index.shift();
                }
                for (k = 0; k < name.length; k++) {
                    s = name[k];
                    name[k] = (s.charAt(0) !== '@')
                        ? new(tree.Keyword)(s)
                        : new(tree.Variable)('@' + s.slice(2, -1), 
                            index[k], env.currentFileInfo);
                }
                return name;
            }
        }
    }
};
return parser;

}; less.Parser.serializeVars = function(vars) {

var s = '';

for (var name in vars) {
    if (Object.hasOwnProperty.call(vars, name)) {
        var value = vars[name];
        s += ((name[0] === '@') ? '' : '@') + name +': '+ value +
                ((('' + value).slice(-1) === ';') ? '' : ';');
    }
}

return s;

};