code: 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);
                  }
              }
docs: 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*.