The ModalEnforcerMorph gives the ability to make any set of Morphs (and
their submorphs) be modal to the rest of the World. Improves on the
standard scheme for doing modality in a variety of ways. Most
importantly, only the modal morphs can recieve mouse and keyboard
events, so you can't click on another system window and bring it in
front of a modal morph that is hogging the keyboard. 

A ModalDialog subclass of SystemWindow is provided, with some example
dialogs (message, confirm, yes/no/cancel).

[Tested on the squeak image updated to #4441 available at
ftp://st.cs.uiuc.edu/pub/Smalltalk/Squeak/.]

To download and/or see a thorough description, go here:
 
http://users.bestweb.net/~swerling/squeak/spsSqueakDocs.html#modalSupport