code: function (token, k) {
          var str = "";
          for (var i = 0; i < k && i < token.length; i++)
              str += token[i];
          if (i < token.length) {
              str += "<";
              str += token[i++];
              str += ">";
              for (; i < token.length; i++)
                  str += token[i];
          }
          return str;
      }
docs: /*  return the tree specification, marked at token k