function closeAll() {

	var allUnorderedLists = document.getElementById("nav").getElementsByTagName("UL");
	for (var i=0; i<allUnorderedLists.length; i++) {
		allUnorderedLists[i].style.visibility = 'hidden';
	}

}


function closeAllRecursive(element) {

	var unorderedLists = element.getElementsByTagName("UL");
	for (var i=0; i<unorderedLists.length; i++) {
		unorderedLists[i].style.visibility = 'hidden';
	}

}


function toggleChildren(ulId, liId) {
	
	var ulElement = document.getElementById(ulId);
	var liElement = document.getElementById(liId);

	// zoek alle LI's onder UL
	liElements = ulElement.getElementsByTagName("LI");
	for (var i=0; i<liElements.length; i++) {
		var closeNode = false;
		if (liElements[i] == liElement) {
			// geklikte element
			var childUlElement = getChildUl(liElement);
			if (childUlElement) {
				if (childUlElement.style.visibility != 'visible') {
					childUlElement.style.visibility = 'visible';
				} else {
					closeNode = true;
				}
			}
		}
		if (closeNode || liElements[i] != liElement) {
			closeAllRecursive(liElements[i]);
		}
	}

}


function getChildUl(liElement) {
	
	for (var i=0; i<liElement.childNodes.length; i++) {
		if (liElement.childNodes[i].nodeName == 'UL') {
			return liElement.childNodes[i];
		}
	}
	return false;

}