code: function readUnit(scanner) {
      var unit = scanner.getTokenValue();
      var backSlashPos = unit.indexOf('\\');
  
      if (backSlashPos > 0) {
          // patch token offset
          scanner.tokenStart += backSlashPos;
  
          // return part before backslash
          return unit.substring(0, backSlashPos);
      }
  
      // no backslash in unit name
      scanner.next();
  
      return unit;
  }
docs: special reader for units to avoid adjoined IE hacks (i.e. '1px\9')