This would be a good discussion for the Prawn mailing list. Post there and I'll reply with some details (and the other devs will likely chime in as well).

Just let us know what sort of feature set you want to implement, and we can point you to the relevant spec sections and supporting materials.

Prawn's source is pretty readable, and will be even more so as we refactor. A trip through the source might help, too:

http://github.com/sandal/prawn