There exists xref-tag->path+anchor.
I don't see the reverse -- anything like "xref-path+anchor->tag".
Is it possible for me to write this myself, and if so, how?
Why I ask: Given a documentation path + anchor, I want to look up a bluebox using fetch-blueboxes-strs, but that takes a tag.
[Why I ask that: I have a documentation path and anchor from check-syntax analysis, and would like to use that -- at a time where I no longer have the original expanded syntax, and therefore can't use xref-binding->definition-tag.
Although it's possible to synthesize some identifier from source text, that's not always reliable.
Although it's possible to eagerly calculate this for all path+anchor annotations, that's wasteful and slow.]