Looks like handling of parsing context for TokenBuffer and TreeTraversingParser is not uniformly handled, leading to issues like #2049. It would make sense to add a test over some basic cases, first, to unify handling; that would reduce need for one-off patching.

Once test(s) added, need to see what fixes are needed, and which can go in 2.10, which 2.11 (or even 3.0 possibly).