[nikita.mmf]

function getParent ( firstElem, secondElem ) {
	var parent;
	while ( parent != document.body ) {
		parent = firstElem.parentNode, child = parent.firstChild; 
		while ( child ) {
			if ( child == secondElem ) { 
				return parent; 
			}
			child = child.nextSibling;
		}
		parent = parent.parentNode;
	}
	return parent;
}

Агоритм не рабочий