I've noticed that I can use the letter x in place of * in wildcard version specifications. Is this expected? If it is expected, should it be documented clearly?

• I have searched the issues of this repo and believe that this is not a duplicate.
• I have searched the documentation and believe that my question is not covered.

Issue

I've been playing around with version contraints and via copy/paste ended up with a requests = "2.x" specification in my pyproject.toml file. I was surprised to see this work, and even more surprised that it appears to be case insensitive and function just like * though using x or X is not documented in the wildcard section of https://python-poetry.org/docs/dependency-specification/

I believe this "support" comes from the regex X_CONSTRAINT in https://github.com/python-poetry/poetry-core/blob/main/src/poetry/core/semver/patterns.py but I haven't fully traced where this behavior comes from. Basically I just want to know if this is actually a supported feature that needs documentation, or if its a "happy accident" somehow?