Stefan Beller [off-list ref] writes:
How would you know(/code) that v1.6.0-rc0~120^2 is a text worth linking?
"v1.6.0-rc0" is a custom string as that is how we name tags in this project.
It can follow any convention in other projects.
Maybe a first approximation is if there is a `~` followed by numbers
or a ^ character, inspect the whole thing if it is a reference into the history?
You (as a gitk process running in a repository) know what tags are
in your repository, so you can find the above pattern and see if the
prefix matches any of the known tag. That way, you do not have to
worry about having to special case HEAD etc.