Make a Plugin API for your REALbasic application
[RBL-0022]

This was well-written and as it says in the description, there were plenty of illustrations, but there is a caveat. I was looking for an RB-only solution, like adding skinning and similar customization, but that is not what the article is about. It uses other software tools to set up real Full-blown APIs. Not exactly what I wanted, but it may be good for you.