I was looking at Twig template parser, used in Symfony, recently and found interesting filter approach used in there.
In Twig filter is after-processing applied to tag result. Basically all our:
- tab removal
is done there as filters. However that concept goes far beyond that - each Twig plugin can define it's own filter, that can be used with ANY OTHER tag from any other module.
Also it's easily provides ability add block tags per module.
I also recommend digging deeper into Twig code to find more ways to organize cross-module communication, e.g. shared tags, shared events.