I would like to implement a kind of portal class where the portal is a 
viewer into a PasteUpMorph which is possibly much larger than the portal. 
The PasteUpMorph is a submorph of the portal (and the portal itself is 
likely a subclass of PasteUpMorph). The portal will have "active borders" a 
few pixels wide. The behavior I want to implement will work like this:

If a drag is started from inside the border, it drags the underlying 
PasteUpMorph with it.

I need some suggestions of code to read as an example of how to do this.

-Thanks in advance, Jim