code: function validateFormat(attr, conf, err) {
      if (nullCheck.call(this, attr, conf, err)) return;
      if (typeof this[attr] === 'string') {
          if (!this[attr].match(conf['with'])) {
              err();
          }
      } else {
          err();
      }
  }
docs: Format validator
  @param {mixed} attr
  @param {mixed} conf
  @param {mixed} err