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.