function initHover(classNameOfHLElement){
	var allHoverElements = getElementsByClass(classNameOfHLElement);
	
	for( i = 0; i < allHoverElements.length; i++){
		allHoverElements[i].onmouseover = buttonOver;
		allHoverElements[i].onmouseout = buttonOut; 
	}
}

//append '_over' to the classname
function buttonOver(){
	this.className += '_over';
}

//remove '_over' from the classname
function buttonOut(){
	this.className = this.className.replace('_over','');
}