@Gargron You're right, I was afraid I'd missed something like this--considering how many spec documents are involved, it wasn't obvious that this rule exists!

I feel that the point still stands in regard to extensions, though (e.g., you have to write `featured` and can't write `toot:featured` with a different context). Technically that's not following the spec, but it's less significant since it's a Mastodon-specific extension.