It's foolish to use a standard well defined very precise but incorrect term of art like like "MIME Type" that is actively misleading to a technical audience of github users who are more likely than most people to know the standard official definition, and which is LESS commonly known than a correct widely understood vernacular term like "file name extension", if your goal is to be understood by everyone.

I'd rather a technically oriented site like github be "unrealistic" and correct and instructive, than foolish and wrong and misleading. Are you really saying it's better to use the wrong term because github users might not understand the more widely known correct term?

Just how does leading the user on a wild goose chase looking up the definition of "MIME Type," causing them to waste their time and misunderstand the error message, when it's really a file name extension (a term which more people understand anyway), help the user achieve their goals?

The bottom line is that github disallowing "MIME Types" or "file name extensions" in user names, just like a bank disallowing "select" and "drop" and "from" and "null" and "delete" and "bobby" and "tables" in passwords, is a symptom of a much larger more terrible problem, and whoever wrote that stupid error message instead of fixing the underlying bug that caused it has much worse problems than poor English language writing skills.

Muphry's law strikes again!

The bug affected Gitlab, not GitHub.

Sorry, I thought you were referring to the bug reporter rather than the author of the error message itself, in the latter case I agree.

The bug reporter merely copies the incorrect error that gitlab gave him; The issue here is that someone working in login / security of gitlab doesn't know what a mime type is. That is extremely worrying - it's not a part of the code where you can afford to be sloppy.

It's a very odd error. Apparently .nro is a file extension used by the Nintendo Switch video game console; .o is obviously the output of compilers, so I'm not sure why my username wasn't rejected. Maybe it would be if I tried to register now.