Currently the namespace protection table on https://en.wikipedia.org/wiki/Special:ListGroupRights shows something like this
Namespace | Right(s) allowing user to edit |
---|---|
MediaWiki | Edit the user interface (editinterface) |
Gadget | Edit gadget JavaScript and CSS pages (gadgets-edit) |
Gadget definition | Edit gadget definitions (gadgets-definition-edit) |
Therefore it assumes all users with (editinterface) permission (sysop for instance) can edit all pages in MediaWiki namespace. This was true before, but not any longer. (editinterface) alone is not sufficient to edit for example https://en.wikipedia.org/wiki/MediaWiki:History_copyright