    paper.localToClientRect(rect)

Transform the rectangle `rect` defined in local coordinate system to the client coordinate system.

    var bbox = element.getBBox();
    var clientRect1 = paper.localToClientRect(bbox);
     // alternative method signature
    var clientRect2 = paper.localToClientRect(bbox.x, bbox.y, bbox.width, bbox.height);
    // Draw an HTML rectangle above the element.
    var div = document.createElement('div');
    div.style.position = 'fixed';
    div.style.background = 'red';
    div.style.left = clientRect1.x + 'px';
    div.style.top = clientRect1.y + 'px';
    div.style.width = clientRect1.width + 'px';
    div.style.height = clientRect1.height + 'px';
    paper.el.appendChild(div);