code: function() {
      var captures;
      if (captures = /^u\+[0-9a-f?]{1,6}(?:-[0-9a-f]{1,6})?/i.exec(this.str)) {
        this.skip(captures);
        return new Token('literal', new nodes.Literal(captures[0]));
      }
    }
docs: 'U+' [0-9A-Fa-f?]{1,6}(?:-[0-9A-Fa-f]{1,6})?