/**
 * Requires the Prototype JavaScript framework of version 1.5.0+.
 */
function initHeader() {
	// Loop navigation link and bind mousein/out events
	bindNavImageSwapTrigger('header_left_nav');
	bindNavImageSwapTrigger('header_right_nav');
}
function bindNavImageSwapTrigger(elemId) {
	var links = $(elemId).getElementsByTagName('a');
	var nodes = $A(links);
	nodes.each(function(node){
		if(node.getAttribute('toggleable')) {
			Event.observe(node,'mouseover',function(){toggleNavImage(node,true)},false);
			Event.observe(node,'mouseout',function(){toggleNavImage(node,false)},false);
		}
	});
}
/**
 * Toggle image for element
 * @param {Element object} Link element. Must have image child element!
 * @param {int} index for this element
 * @param {boolean} if true display "on"-image, else "off"-image
 */
function toggleNavImage(elem,on) {
	if(!elem) return; // Illegal case
	var img = elem.getElementsByTagName('img');
	if (!img) return; // Illegal case
	var img_src = img[0].src;
	// Swap image source
	if(on) {img_src = img_src.replace(/_off./,'_on.');} 
	else {img_src = img_src.replace(/_on./,'_off.');}
	img[0].src = img_src;
}