Note: This is not a new suggestion. See forum #268394 and issue #6088. But this idea still has potential so I'm throwing it back into the spotlight.
Context
People are currently trying to deal with the Arknights copytag situation in topic #35072.
For those unaware: Arknights is a 5+ year old game in an established universe with +200k posts. Arknights: Endfield is a recently launched game that takes place in the same universe but with a 100-500 year timeskip. Arknights: Endfield implies Arknights which has converted this tag into an catch-all for both games. People searching specifically for Arknights content will need to filter their results, but a new umbrella tag like arknights_(series) will undoubtedly end up as a dumping ground. A new type of tag could help here: Abstract Tags.
The name is derived from an Abstract Class a concept in Objected-oriented programming. In a nutshell, an abstract class is used as a blueprint for other classes but cannot be used by itself.
How would it work?
Abstract tags would function very similarly to deprecated tags; They cannot be added by adding them though the edit field.
They would however still be able to be added through an implication. In a visual way:
fruit (abstract) | +-- apple | +-- banana
I wouldn't be able to tag a post with fruit but if I tag banana, it would automatically add fruit.
Going back to the Arknights situation:
Arknights could then be cleaned up to apply to the original game exclusively and Arknights: Endfield would be pretty much unchanged. Both these tags would then imply a new umbrella tag.
Note that because this umbrella is managed exclusively through implications, the naming and findability for tagging specifically doesn't really matter. We could name it arknights_cinematic_universe, amiyaverse whatever distinctive name we need.
In short, abstract tags would force users to be a bit more specific.
What about other copyrights?
The functionality of Abstract Tags would also add a way to deal with people only slapping the *_(series) tag on a post and calling it a day.
naruto_(series) copytags:1 / lyrical_nanoha copytags:1 / monogatari_(series) copytags:1 / splatoon_(series) copytags:1 / fate_(series) copytags:1
For example:
The uploader of this post just tagged it with Monogatari (Series) and pressed post.
Ononoki Yotsugi was introduced in Nisemonogatari so at the very least that tag should have been included.
Ideally all copyrights where the character appeared should be included as tags.
Usage with general tags
There are also a number of general tags with implications where the umbrella tag ideally should always be accompanied by atleast 1 child tag.
Here a non-exhaustive list (that is up for discussion) where Abstract Tags could help out:
frills
frills -frilled_*
Main discussion in topic #25849. Frills are attached to something, for which we have proper tags.
multiple girls
multiple_girls -2girls -3girls -4girls -5girls -6+girls
Multiple girls means two or more, so one of these tags should be included.
multiple boys
multiple_boys -2boys -3boys -4boys -5boys -6+boys
Same reason as above.
breasts
breasts -small_breasts -medium_breasts -large_breasts -huge_breasts -gigantic_breasts
Besides the various action tags that imply breasts, their size should be quantified.
pov
pov -pov_* -*_pov
POV requires a part of the viewer be visible, we have several tags for that.
facial hair
facial_hair -beard -*beard* -mustache -*mustache* -mutton_chops -sideburns -*sideburns* -stubble -*stubble* -soul_patch -goatee -*goatee* Not a perfect search, but I'm hitting the limit here
I think tagging just facial hair isn't really that helpful when we have so many facial hair related tags.
mole
mole -mole_*
A mole is always located somewhere on a body. We have fitting tags for pretty much all of them.
genderswap
genderswap -genderswap_(*
A genderswap should always include a direction. MTF / FTM / OTF / OTM / FTO / MTO
And a bonus meta tag: traditional media
traditional_media -*_(medium)
If it's known that a post is traditional media, then the uploader should also specify which form specifically.
Thoughts?

