Manual:$wgRestrictionLevels

Details
Set of permission keys that can be selected on the 'page protection' page. 'autoconfirm' allows all registered users if $wgAutoConfirmAge is 0.

If you add additional levels (e.g. 'docwriters') those can be named via editing the content of 'MediaWiki:Protect-level-docwriters'.

Don't forget to adjust your group permissions accordingly; e.g.: $wgGroupPermissions['docwriters']['docwriters'] = true; $wgGroupPermissions['sysop']['docwriters'] = true;