It's not just when we release, but as soon as it goes to master, anyone who might be using master needs to know.

To answer Paul Price: I did not find any instances of "config" used as a variable inside config override files. That means in theory we could continue to support root for backwards compatibility, while also supporting config. Doing just that much is trivial, but not adequate. To do it right we need to warn users when they load an outdated config override file, and I have not figured out how to do that.

My inclination is to make a hard break. Converting config override files is easy.

I agree about a hard break (though it may be controversial). I was more worried about breaking things if someone was using config inside an override file already.

I found a safe way to support root:

• try loading the override file using "configure"
• if that raises NameError and the exception contains "root" (which is what happens if the file uses "root" instead of "config) then print a warning and try again, using "root".

This seems safe to me. It will work with files that use "root" and contain a variable named "config". Similarly it will work for files that use "config" but contain a variable named "root. The only way I think it can cause problems is if the config override file has an error and the resulting message is a NameError whose message contains "root". In that case I would expect it to try loading again with "root" (which it should not do) and to fail with a confusing error message.

I think we should remove this backwards compatibility code at some point, but give people some time to update their personal config files first.

Yusra AlSayyad Thank you very much for the review.

Regarding the two config files: you were right that I had corrupted them. The value of defaultRoot should be "/lsst/DC3root" in both cases.

Regarding pex_config:python/lsst/pex/config/config.py I agree that the documentation is confusing. I took a cleanup pass on all doc strings for the Config object. I hope it is clearer now. (Field still needs such a pass, but I found enough bits that I didn't understand that I decided to leave it alone.)