I'm in Oslo right now and we're working out (and implementing) new features in TAP. One of them is the new YAML diagnostics. They look like this (these aren't all we support):
not ok 2 We ain't got foobar!
Again, this is is sample and incomplete (and optionally available on successful tests).
Currently you can shove anything in there you want, but you must use upper-case keys for your personal use and all lower-case keys are reserved (but it's not a parse error to use an unknown lower-case key since we will add keys in the future). Are there any strange Unicode issues where we might get confused about what is upper and lower case?)
For the curious: tags may be anything you want. There are no constraints, but the parser will be able to return results by tags. We may very well allow a "tag constrained" test run which will still run all tests, but only report results per tag. We could potentially even run all tests and separate out results per tag. Lots of possibilities here and we're just barely beginning to appreciate the benefits.
We're implementing this at a low-level right now, but we don't yet have an exposed API.