// UTILITIES

// add event to the document
// example: addEvent(window, "load", fnc, false);
function addEvent(elm, evType, fn, useCapture) {
	if (elm.addEventListener)
	{
		elm.addEventListener(evType, fn, useCapture);
		return true;
	}
	else if (elm.attachEvent)
	{
		var r = elm.attachEvent('on' + evType, fn);
		return r;
	}
	else
	{
		elm['on' + evType] = fn;
	}
}

// viewable screen area : height
function getViewportHeight()
{
	if (window.innerHeight != window.undefined) return window.innerHeight;
	if (document.compatMode == 'CSS1Compat') return document.documentElement.clientHeight;
	if (document.body) return document.body.clientHeight; 
	return window.undefined; 
}