Detecting a "grabEnter"?

[David Epstein]

Is there a way to capture "drag" events once an object has been  
"grabbed" with the "grab" command?

I know that by setting the dragData I can initiate a dragDrop, and  
then capture events like "dragEnter". But in that case the user is  
just dragging a cursor around. If we're actually dragging a control,  
it seems that the only message sent is mouseMove.

If, for example, I want to highlight the "object-that-will-be-dropped- 
on-if-the-mouse-is-released now," that would seem to require checking  
the rect of all possible objects on every nudge of the mouse-- 
particularly onerous if the possible objects are numerous and their  
locations are changeable.

Is there a more efficient solution? (I notice in the message watcher  
that when an object is grabbed, a dragStart message is sent; but I  
don't detect anything like dragEnter during the course of dragging  
the grabbed object).

Many thanks.

David Epstein