The documentation for 0.12.0 claims that valid tag ids support alphanumeric characters, and - or _.
However, today (on bupstash-0.12.0) tags with hyphens like extracted-from were not working until I changed them to underscores _. Either the documentation should be updated or the pattern should be fixed (preferably the later).
This took a long time to figure out because bupstash gives poor error messages when flags, tags, and positional arguments are mixed up.