public DockingMultiUpdate(IDockingElement dockingElement)
{
// Must provide a valid docking element reference
if (dockingElement == null)
throw new ArgumentNullException("dockingElement");
// Inform docking elements that a multi-part update is starting
_dockingElement = dockingElement;
_dockingElement.PropogateAction(DockingPropogateAction.StartUpdate, (string[])null);
}