I was researching how two characters interact each other, using post and tag data by API.
Then I faced the problem that I can't get whether A pets B or B pets A in the post that has tags "character:A", "character:B", and "petting". (I can make more explicit examples but I'll stop)
How can I get the right relation of these two character? Or if I can't, is there a plan to make tag system that can tell who's petting?

I'm glad if you tell me related forum topic, thanks :)

Nah, that's really not a thing you can currently do, unfortunately. Well, maybe with a much more complicated list of tag search parameters than I'm clever enough to figure out, but... *Shrug.* To the best of my knowledge, using tags to specify which character is doing the thing to the other character, cannot currently be done. ...for the most part...

You can't get that information because the tagging system simply isn't set up in a way to allow you to relate tags like this.
You can use tags like male_penetrating_female (though you'll often find posts that lack it), but there are no combo tags for "petting".

Yeah there are tags having relation between two form in post like male_penetrating_female but it's not for two characters like A_(character)_penetrating_B_(Character).

I'm considering to post a feature request though tag system will be way complicated if it's accepted and I don't know if it's worth it.
Thanks for answering you two!