public function addMfClasses(DOMElement $el, $classes) {
		$existingClasses = str_replace(array("\t", "\n"), ' ', $el->getAttribute('class'));
		$existingClasses = array_filter(explode(' ', $existingClasses));

		$addClasses = array_diff(explode(' ', $classes), $existingClasses);

		if ( $addClasses ) {
			$el->setAttribute('class', $el->getAttribute('class') . ' ' . implode(' ', $addClasses));
		}
	}