Command-Handler Interface for AutoLayout, provides an interface for page-items to respond to certain events. It is similar to EventHandler but it sits in special PageItem bosses (instead of widgets) and only responds to certain events. (In fact this interface is introduced for double click on pageitems only, define it this way just for extensibility consideration. ) It does intend to replace or handle these events.
The event on pageitems is caught by LayoutEventHandler(IEvent *pEvent), which will ask ILayoutControlViewHelper to QueryHitTestPageItemNew and get the pageitem. From the pageitem get this Interface to do any actions.
See also IEventHandler.h