This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.
Your link says
and "Canon!Harry" or "HPMOR!Quirrell" is not trait!character, it's world!character which maps to bang paths very well.
Besides, the tendrils of old hacker culture burrow deep into the fabric of memespace... 8-)
Incidentally, the magma computer algebra system uses ! for casting. This is possibly related.