See, that makes no sense to me. Is the font named "Source Code Pro" or "Source Code Pro for Powerline"? And if I'm using a different font, how do I know what it's name is? For example, is M+ named "M+", "M +", M+ for Powerline" or what exactly?
Yeah, I can see where one could get confused. I use a version of Source Code Pro that's been patched to work with vim-airline[0], which is why it's "for Powerline". On OS X I think you can get the font name from the "Family" column of the Fonts pane, or via Quick Look in the Finder.