Group naming restrictions / guidelines

I've just wasted quite some time figuring out that a '/' is not allowed in group names.
I've been searching, and I can't find any limitations / restrictions / rules / guidelines regarding group names anywhere.

* Max length?
* Allowed chars
* ...

Please advice

Start by searching the existing Azure Web PubSub documentation for group-name guidance and compare it with the reported restriction that '/' is disallowed. Document the maximum length, allowed characters, and other confirmed naming rules, including a clear reference to where users can find them. No files or tests are named in the issue.

Written by the indexing model from the issue text.