<?php
recorre(array(
	'a',
	'b',
	'c' => array(
		'a',
		'b',
		'c',
		'd' => array(
			'a',
			'b' => array(
				'a'
			),
			'c'
		)
	),
	'd'
));
 
function recorre($a){
	if(!is_array($a))
		echo 'String: '.htmlspecialchars($a, ENT_QUOTES, 'ISO-8859-1').'<br />';
	else{
		foreach($a as $b)
			recorre($b);
	}
}
 
/*
String: a
String: b
String: a
String: b
String: c
String: a
String: a
String: c
String: d
*/