Feature request discussion: multi-tag aliases

As per forum #29911, it seems like we have reached the point where the ability to do more complex aliases and implications, chiefly the ability to alias a tag to multiple resulting tags, is needed. Albert?

Incidentally, that will also need some UI discussion about the presentation of such aliases, and I'd like to use this opportunity to discuss another, minor enhancement: wiki pages for tags already say "This tag has been aliased to X". Could we also have it the other way around, ie. "This tag is the target of an alias from Y"? It'd be particularly helpful for discovering shorthand aliases for unwieldy/common tags, such as /trad, /t and /tt.

I'm not sold on the idea. First of all, we need to work out the semantics of multi-tag aliases and how they relate to normal aliases and implications. In set theory terms, A implies B means that A is a proper subset of B, while A aliased to B means that A is exactly equivalent to B. What exactly does A alias B, C mean?

I suppose it means that A is equal to the intersection of B and C (e.g., ;p = wink + :p). The problem is, very few tags truly have this relationship. Strictly speaking, ;p is merely a subset of the intersection of wink and :p, and we already have implications to handle subset relations.

I can't think of many tags that are truly the intersection of multiple other tags. The closest I can come up with is twincest. Twincest is equivalent to the combination twins + incest, and there is (almost) never a situation in which a post would be tagged twins and incest but not twincest, so a multi-tag alias could be used in this situation. With ;p, there are situations in which something could be tagged :p and wink but not ;p, so conceptually it's not correct to alias ;p to :p + wink because :p + wink is not equivalent to ;p.

葉月 said:
Could we also have it the other way around, ie. "This tag is the target of an alias from Y"?

This would be a good idea. Actually it gives me another idea: how about listing the tags implying a given tag in the sidebar when searching for that tag? It'd look something like this. This could help you narrow down your search to more specific tags that you may not be aware of.