I don't understand why you have been downvoted for asking "why m_?". Is everybody on here supposed to know everything about everything, else you get downvoted into grey unreadability?

Personally, I think that bashing/penalizing ignorance (and I mean the word ignorance literally, as being uninformed about a topic, no offense here whatsoever) is one of the lowest forms of abuse. It says much more about the downvoter than it does about the downvoted. And this not even considering the fact that searching online for "m_" isn't going to help you answer your own question.

If everybody just downvoted the questions they deem unworthy of an answer because "you are supposed to know this", there would be no questions answered.

Sorry for the OT.