Comments in the PR. I guess I didn't make the requirements clear enough. The intent is for this to implement defineAlias as described on Data Butler, including use of an alias within a longer dataset type name (which is not explicitly called out on that page).

Not sure if you're ready for a re-review, but I added some comments in the PR. While I think it would be nice to shrink the test data down to something more minimal, it's kind of too late now, so I'm OK with leaving it.

Please announce the availability of this feature in the DM Notifications category on c.l.o. You can point to the doxygen documentation. And the same text (not including the documentation) is likely what Jacek will need for release notes.