Valid names for MQTT items

some days ago I found some doc that states these names must begin with an ALPHA character and must not contain hyphens. Now I do not find that doc anymore (not even in browser history).

Can someone confirm how valid names should look like?

Example that does not work:

testfh/dallassensor_data {"99-A234-5678-0000":20.0}

And this works:

testfh/dallassensor_data {"D99A23456780000":20.0}

The discovery strings are adjusted accordingly.

Thanks a million, Dieter Fauth