<?php

	function validate_xml($source) {
		if ($source == '') return true;

		$document = new DOMDocument();
		$fragment = $document->createDocumentFragment();

		return @$fragment->appendXML($source);
	}

	$source = @$_POST['source'];
	$valid = (validate_xml($source) ? 'yes' : 'no');

?>
<form action="" method="post" style="width: 60em">
	<textarea name="source" style="height: 40em; width: 100%;"><?php echo htmlentities($source); ?></textarea>
	<div>
		<button style="float: right;" type="submit">Validate</button>
		<span>Valid: <?php echo $valid; ?></span>
	</div>
</form>