whole_func_string: 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();
              }
          }
      };
  }
func_code_string: 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();
              }
          }
      };
  }
func_documentation_string: 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.