code: function () {
          if (this.done) {
              return this.EOF;
          }
          if (!this._input) {
              this.done = true;
          }
  
          var token,
              match,
              tempMatch,
              index;
          if (!this._more) {
              this.yytext = '';
              this.match = '';
          }
          var rules = this._currentRules();
          for (var i = 0; i < rules.length; i++) {
              tempMatch = this._input.match(this.rules[rules[i]]);
              if (tempMatch && (!match || tempMatch[0].length > match[0].length)) {
                  match = tempMatch;
                  index = i;
                  if (this.options.backtrack_lexer) {
                      token = this.test_match(tempMatch, rules[i]);
                      if (token !== false) {
                          return token;
                      } else if (this._backtrack) {
                          match = false;
                          continue; // rule action called reject() implying a rule MISmatch.
                      } else {
                          // else: this is a lexer rule which consumes input without producing a token (e.g. whitespace)
                          return false;
                      }
                  } else if (!this.options.flex) {
                      break;
                  }
              }
          }
          if (match) {
              token = this.test_match(match, rules[index]);
              if (token !== false) {
                  return token;
              }
              // else: this is a lexer rule which consumes input without producing a token (e.g. whitespace)
              return false;
          }
          if (this._input === "") {
              return this.EOF;
          } else {
              return this.parseError('Lexical error on line ' + (this.yylineno + 1) + '. Unrecognized text.\n' + this.showPosition(), {
                  text: "",
                  token: null,
                  line: this.yylineno
              });
          }
      }
docs: return next match in input