Tags were a different name for modern categories. This is an archived version of an older idea hypha. In the end, we went with the first proposal with the plan to expand to the third one.
What is a tag?
The way social media does it is not for Mycorrhiza. The way Obsidian does it is the same (and it doesn't fit it too, actually).
A tag is a label that a hypha has. You can see all hyphae that have the given tag.
That's the classic meaning many systems have. They may have different names, but the idea is the same.
Proposals
There are different approachs to the problem. I'll list them here.
Proposal n° 1: primitive
You can add any number of tags to a hypha. You can see all hyphae tagged with a tag. By definition.
Simple, but lacks the vibe. There are no problems with it.
Proposal n° 2: hyphal
You can add any number of tags to a hypha. You can see all hyphae tagged with a tag. Tags are hyphae too.
Problem n° 1. What is a tag-hypha? Is it a different kind, just like media hyphae and textual hyphae? Can a tag-hypha be empty. Problems arise in different areas when we start answering these questions. They are left as an exercise to the reader.
I do not list the rest of the problems, because they follow from the first one. Trust me, there are many of them.
Proposal n° 3: mixed
You can add any number of tags to a hypha. You can see all hyphae tagged with a tag.
You can optionally bind a hypha to a tag. Their names may not match. On the tag's page, the bound hypha is shown as description. Only textual and media hyphae can be such bound hyphae.
Comparison
Proposal n° 2 is the cutest and most vibeful, but sadly, will be a source of annoyance if implemented. Proposals n° 1 and n° 3 will work. I like the third one more, we'll go with it unless a problem is found.
There's still a problem with any proposal. How exactly tags are better than backlinking? When should they be used?