code: function _checkCharsetRange(node) {
    node.ranges=K.sortUnique(node.ranges.map(function (range) {
      if (range[0]>range[1]) {
        throw new RegexSyntaxError({
          type:"OutOfOrder",
          lastIndex:range.lastIndex,
          message:"Range ["+range.join('-')+"] out of order in character class!"
        });
      }
      return range.join('');
    }));
  }
docs: check charset ranges out of order error.(Because of charsetRangeEndEscape) [z-\u54] had to defer check