Anytime the content of a page changes, a new version is generated.
Each Wiki page keeps track of past versions, and allows you to view past versions,
as well as revert back to a past version.
Click on the "Past Versions" icon in the page sidebar, to bring up the versions screen.
From there, select a desired version on the right side to view the content of that
page from that version. Clicking on the "restore" button will revert back to that version.
Versions only encompass the actual page content & title of a page.
This means comments, labels, attached files, and page permissions live
outside of the versions, and they remain as they currently are,
even if you revert back to a version.