Is MW >= 1.22 a requirement? If so we can check wgVersion and throw an exception

http://www.mediawiki.org/wiki/Extension:VisualEditor says yes.

I'm not familiar with how extensions usually check for MW version compatibility. Obviously we could do it in the client and throw a JS exception, but there may a preferred way in PHP?

Digging around I assume wfUseMW( '1.22alpha' )?

Change 76706 had a related patch set uploaded by Esanders:
Check MW version before loading VE

https://gerrit.wikimedia.org/r/76706

Change 76706 merged by jenkins-bot:
Check MW version before loading VE

https://gerrit.wikimedia.org/r/76706

Change 76869 had a related patch set uploaded by Jforrester:
Add dependency check for MW1.22/wmf11

https://gerrit.wikimedia.org/r/76869

Change 76869 merged by jenkins-bot:
Add dependency check for MW1.22/wmf11

https://gerrit.wikimedia.org/r/76869

This is now merged.