array_key_exists

<?php     public function has($key)

    {

        return array_key_exists($key, $this->items);

    }



    public function put($key, $value)

<?php         $ordered = [];



        foreach ($order as $key) {

            if (array_key_exists($key, $array)) {

                $ordered[$key] = $array[$key];

                unset($array[$key]);

            }

<?php                 if (! array_key_exists($array_key, $child)) {

                    $child[$array_key] = [];

                    $has_children = false;

                }