code: function(item, separator, preserveFirstSeparator) {
      const result = [];
  
      if (this.token == separator) {
        if (preserveFirstSeparator) result.push(null);
        this.next();
      }
  
      if (typeof item === "function") {
        do {
          result.push(item.apply(this, []));
          if (this.token != separator) {
            break;
          }
        } while (this.next().token != this.EOF);
      } else {
        if (this.expect(item)) {
          result.push(this.text());
        } else {
          return [];
        }
        while (this.next().token != this.EOF) {
          if (this.token != separator) break;
          // trim current separator & check item
          if (this.next().token != item) break;
          result.push(this.text());
        }
      }
      return result;
    }
docs: Helper : reads a list of tokens / sample : T_STRING ',' T_STRING ...
  ```ebnf
  list ::= separator? ( item separator )* item
  ```