What branch is posted?

Hello! I have a general question that I just cant seem to find the answer to. In the Github Actions main page a Branch is linked to all the runs. Is there a rhyme or reason to which branch is listed? For push events, the base branch seems to be listed, for pull_request events the compare branch seems to be listed. Is there a guide to this somewhere? Thank you!

pull_request seems to show the head branch
pull_request_target and issue_comment show nothing
push shows the branch/tag (if you push a pair of branches for the same sha, you should get two events).