Just saw in recent tread: (https://forum.nim-lang.org/t/4366)
wNim
wFrame
mWhichButton
wOkCancel
wIdOk
and some more.
I guess w may refer to windows or to module author name, for the m I have no idea at all. Maybe it is because Araq likes to use such prefixes for his inpure enums in compiler code. There that may be OK (and generally is at least two letters) but I can't say I like such single letter prefixes for libs like GUI lib that match. (For gintro I avoided prefixes generally, with some rare exceptions like GObject or GMessage. I had no really trouble with name conflicts, and in case of conflict I personally prefer gtk.button over gbutton.)