How to "Turn On" Version Editor in Xcode 4?

How to do so?

What URL is the documentation of version editor?

If I click versi开发者_运维问答on editor toolbutton I just see an empty screen to the right

The quasi-answer (workaround) to your question (I think) is that.. there IS NO such thing as a "turn on" for this feature. If it isn't showing up right - which I've seen many times - means Xcode is having a debatably-temporary mental lapse. Chances are - it (Xcode) is about to crash… but if you just want to be done with it / seal the deal / put the horse out of it's misery, etc..

1. quit Xcode.
2. reopen Xcode.

and you should be able to browse your versions, á la Time Machine, as usual.

EDIT Ripley's believe it or not ® I think I'm wrong!

More likely is that your git "arrangement" has become "f-ed up", somehow-or-other.

For me no amount of committing in the GitHub client for Mac would remedy the situation (for some files)… However, thanks to this hint, i guess forcing Xcode to "take a good, long look at itself in the mirror" via the "actual" Xcode File -> Source control => commit command does seem to bring back the version-editing functionality of problematic source files.