var tag = document.getElementById("tag");
var d = new DraggableObject(tag);
d.customMouseMove = function(event) {
	// dragStart[XY] is position relative to tag at the start of dragging
	// event.page[XY] is current position, relative to the top left corner of the page
	var left = event.pageX - this.dragStartX;
	var top = event.pageY - this.dragStartY;

	// this.domNode is a reference to tag
	// this code assumes tag has absolute positioning
	this.domNode.style.left = left + "px";
	this.domNode.style.top = top + "px";
};
d.customMouseUp = function(event) {
	// this will tell you exactly where the mouse was when you released the button
	alert([event.pageX, event.pageY]);
};