Hmm, you do make some good points and I appreciate it. However, I don't know that I'd want to pull the plan out of the grammar as one could use that to easily write some code to parse a bunch of regular TAP strings to validate their TAP producer. At that point, the only required semantic check would be to ensure that test numbers correspond to the correct test line. That would make semantic analysis much simpler since the grammar, as a declarative tool, is more likely to be correct.

I like the rest of what you've done, though. Still, maybe I'm just smoking crack :)