Code to check for a key inside a deep array

array-deep-key-search.php

<?php
// Deep search array for key.
function multi_key_exists( array $arr, $key ){
	// is in base array?
	if ( array_key_exists($key, $arr) ) return true;

	// check arrays contained in this array.
	foreach ( $arr as $element ) {
		if ( is_array( $element ) && multi_key_exists( $element, $key ) ){
			return true;
		}
	}

	return false;
}