[gnat]

Is there much written about the architectural models that enable this kind of customisation. This is highly relevant to my life right now, and I'm struggling to find much to read about how to build a core product that's extensible by third parties. The Apache web server, with its request lifecycle and chained handlers, is my mental model for that. But there must be other models too, and I'd like to see them described in the hopes that one leaps out as a good fit for our product and market.