Constraining 'grab'

[Ken Norris (dialup)]

Hello,

With all the jabber about mouse functions, I'm almost afraid to ask this
question:

If it's unwise to use 'the mouse' repeats to do it, then...How do I
constrain 'grab' to a rect (or any other) boundary?

Know what I mean? I don't want the user to drag the object out of bounds. I
looked through the docs and couldn't find an example.

Best regards,
ken N.