I think I've figured out how to do that, but I can't figure out how to make my forms use the subclass...

I've even tried directly modifying the actual base class (after backing it up twice! Honest!) and I can't get the behaviour 'inherited' - what am I not doing?
(Just tried to make it set a variable in the gotfocus of the textbox class and then waited expectantly for the variable to appear in my recompiled forms on entry to any of my textboxes... no joy)

and where is the definitive idiot level guide to these issues?

Harry