/**
 * @return [x,y] - position of the upper-left corner of node relativ to the 
 *                 upper-left corner of the page
 */
function getPageRelativePosition(node) {
    var result = [0,0];
    while (node) {
        result[0] += (node.offsetLeft - node.scrollLeft);
        result[1] += (node.offsetTop - node.scrollTop);
        node = node.offsetParent;
    }
    return result;
}