First, I don't understand how a new link-type is
registered with the system.
Being a subclass of PRLink is enough. See the class-side of the PRLink
hierarchy for details.
Secondly, in general, I'm not clear on how to
extend the markup system. Are
their specific places I should look to get a better understanding of this?
Is there some kind of overview of the internal
organization of the markup
system that will help guide me in how it all works together?