<?xml version="1.0" encoding="ISO-8859-1"?>
<root>
	<first_item>Test 1st item</first_item>
	<first_level_nested>
		<item idx="0">value #1</item>
		<item idx="1">value #2</item>
		<second_level_nested>
			<item idx="0">value #3</item>
			<item idx="1">value #4</item>
		</second_level_nested>
	</first_level_nested>
	<second_item>Test 2nd item</second_item>
</root>

Array
(
	[root] => Array
	(
		[first_item] => Test 1st item
		[first_level_nested] => Array
		(
			[0] => value #1
			[1] => value #2
			[second_level_nested] => Array
			(
				[0] => value #3
				[1] => value #4
			)

		)

		[second_item] => Test 2nd item
	)

)

<?php

function xml_decode($output) {
	$xml_parser = xml_parser_create();
	$xml_callback = new XmlCallback();
	
	if (!xml_set_element_handler(
		$xml_parser,
		array($xml_callback, 'startElement'),
		array($xml_callback, 'endElement')
	)) throw new Exception('xml_set_element_handler() failed');
	if (!xml_set_character_data_handler($xml_parser, array($xml_callback, 'data'))) {
		throw new Exception('xml_set_character_data_handler() failed');
	}
	if (!xml_parser_set_option($xml_parser, XML_OPTION_CASE_FOLDING, 0)) {
		throw new Exception('xml_parser_set_option() failed');
	}
	
	if (!xml_parse($xml_parser, $output, TRUE)) {
		$xml_error = sprintf(
			"%s at line %d",
			xml_error_string(xml_get_error_code($xml_parser)),
			xml_get_current_line_number($xml_parser)
		);
		throw new Exception("XML error: $xml_error\nXML data: $output");
	}
	
	xml_parser_free($xml_parser);
	
	return $xml_callback->getResult();
}

class XmlCallback {
	private $ret = null;
	/* assign and use references directly to the array, or else you'll be in trouble */
	private $ptr_stack = array();
	private $level = 0;

	public function __construct() {
		$this->ptr_stack[$this->level] =& $this->ret;
	}

	public function startElement($parser, $name, $attrs) {
		if ($name == 'item' && isset($attrs['idx'])) {
			$name = $attrs['idx']; /* reconstruct arrays with numeric indexes */
		}

		if (!isset($this->ptr_stack[$this->level])) {
			$this->ptr_stack[$this->level] = array();
			$this->ptr_stack[$this->level][$name] = null;
		} else {
			if (!is_array($this->ptr_stack[$this->level])) {
				if (!strlen(trim($this->ptr_stack[$this->level]))) {
					/* if until now we got only whitespace (thus scalar data),
					but now we start a nested elements structure, discard this
					whitespace, as it is most probably just space between the
					element tags */
					$this->ptr_stack[$this->level] = array();
				} else {
					throw new Exception('Mixed array and scalar data');
				}
			}
			if (isset($this->ptr_stack[$this->level][$name])) {
				/* isset() == (isset() && !is_null()) */
				throw new Exception("Duplicate element name: $name");
			}
		}

		/* array_push() */
		++$this->level;
		$this->ptr_stack[$this->level] =& $this->ptr_stack[$this->level-1 /* MINUS ONE! */][$name];
	}

	public function endElement($parser, $name) {
		if (!array_key_exists($this->level, $this->ptr_stack)) {
			throw new Exception('XML non-existing reference');
		}

		/* array_pop() */
		unset($this->ptr_stack[$this->level]);
		--$this->level;

		if ($this->level < 0) throw new Exception('XML stack underflow');
	}

	public function data($parser, $data) {
		if (is_array($this->ptr_stack[$this->level])) {
			if (strlen(trim($data))) { # check if this is just whitespace
				throw new Exception('Mixed array and scalar data');
			} else {
				/* we tolerate AND skip whitespace, if we're already in
				a nested elements structure, as this whitespece is most
				probably just space between the element tags */
				return;
			}
		}
		if (is_null($this->ptr_stack[$this->level])) {
			$this->ptr_stack[$this->level] = ''; /* first data input */
		}
		$this->ptr_stack[$this->level] .= $data; /* we may be called several times, in chunks */
	}

	public function getResult() {
		return $this->ret;
	}
}