Zoom in on UML Packages

["Donald A Pellegrino" <Donald A Pellegrino USA dupont com>]

I think it would be nice if I could select a Package in a UML diagram and
give some command to get Dia to open another UML diagram for that Package.
It would probably be necessary to modify the Package widget so that it
would have a "filename" property to associate a .dia file with the
individual package.  Then there would need to be command added to the
context menu and maybe given a shortcut key.

Does this seem like a good idea?

Where should I look in the code to go about adding this feature?