function tree_toggle(event) 
{
	event = event || window.event
	var clickedElem = event.target || event.srcElement

	if (!hasClass(clickedElem, 'Expand')) {
		return 
	}

	var node = clickedElem.parentNode
	if (hasClass(node, 'ExpandLeaf')) {
		return 
	}

	var newClass = hasClass(node, 'ExpandOpen') ? 'ExpandClosed' : 'ExpandOpen'
	var re =  /(^|\s)(ExpandOpen|ExpandClosed)(\s|$)/
	node.className = node.className.replace(re, '$1'+newClass+'$3')
}


function hasClass(elem, className) {
	return new RegExp("(^|\\s)"+className+"(\\s|$)").test(elem.className)
}