code: function invokeArrayArg(arg, fn, context) {
    if (Array.isArray(arg)) {
      arg.forEach(context[fn], context);
      return true;
    }
    return false;
  }
docs: if the argument is an array, we want to execute the fn on each entry
  if it aint an array we don't want to do a thing.
  this is used by all the methods that accept a single and array argument.
  @param {*|Array} arg
  @param {String} fn
  @param {Object} [context]
  @returns {Boolean}