The project wiki is a source code repository so has version history, tags and branches but this is not exposed in any useful way in the UI.
For projects who want to maintain their documentation on the wiki this makes it tricky to easily maintain multiple versions of the documentation for different versions of the project because we can't easily expose these to users.
It would be great if when your wiki has more than one tag/branch in it the UI would allow you to switch between different versions of the wiki. That way users can be pointed to the documentation for version X.
Currently the only way to achieve this appears to be to clone the wiki and push it into a new project representing the documentation for a specific version of your project which is ugly to say the least.