[wp-hackers] doing validations at save/update time. advise is needed.

[Haluk Karamete]

What's a good plug-in that taps into the update post or save post
action that allows admins to enforce rules such as if a user selects a
category with the ID 5 then he also has to select at least one
category from the the XYZ custom taxonomy etc - or that update/save
won't go thru.

I'd like to write my own rules as to who ( which roles ) can do what and so on.

My plan is this. Get a well-written plug-in and use that as the boiler
plate for customizations. So, I can just go into the source code of
that plug in and inject all kinds of business logic that is specific
to my web site.

Any leads towards this goal is really appreciated.