function toggleMenu(evt) {
	var e = new xEvent(evt);
	var obj = e.target;
	if(obj.nodeName != 'BUTTON') return;

	var node_srl = obj.className.replace(/^menu_/,'');
	if(!node_srl) return;

	var li_obj = xGetElementById("menu_parent_"+node_srl);
	if(!li_obj) return;
	var className = li_obj.className;

	if(/nav_tree_off/.test(className)) {
		xInnerHtml(obj,'-');
		li_obj.className = className.replace(/nav_tree_off/,'nav_tree_on');
	} else {
		xInnerHtml(obj,'+');
		li_obj.className = className.replace(/nav_tree_on/,'nav_tree_off');
	}
}

xAddEventListener(document, 'click', toggleMenu);