code: function verifyImplementations(interfaces, target) {
      for (var
        current,
        key,
        i = 0; i < interfaces.length; i++
      ) {
        current = interfaces[i];
        for (key in current) {
          if (hOP.call(current, key) && !hOP.call(target, key)) {
            warn(key.toString() + ' is not implemented');
          }
        }
      }
    }
docs: basic check against expected properties or methods used when `implements` is used