Organization of the plugin system. Where to start?

Question

CMS

How to start implementing a plugin system in a self-written CMS?
I am working with php at the moment, but the language is not so important, in principle, theory and best practices are more interesting. php, ruby, js will do. python would be interesting too.
Where can I read literature, in which cms\frameworks can I see a good implementation, where to start?
Clarification: the desire to find the simplest solution gives the following result:
The user submits a request
All included plugins are loaded, an array of routes is formed from them.
When the router looks for where to send the request, first it looks into the plugins, then into the routes of the framework itself.
That, in fact, is the whole point, what can be the non-obvious tricks of such a simple solution?

Answer 1

www.stackoverflow.com/a/217706

Answer 2

there are quite a few interesting things on Laravel that will help you with the current task.