code: function (type, exp1, exp2) {
        var result;
  
        switch (type) {
          case '&':
            result = exp1.toString() + exp2.toString();
            break;
        }
        return result;
      }
docs: match special operation
  @param {String} type
  @param {String} exp1
  @param {String} exp2
  @returns {*}