Manual:$wgAddGroups

From MediaWiki.org

Access: $wgAddGroups
Controls who can add specific groups using Special:Userrights.
Introduced in version:	1.11.0
Removed in version:	still in use
Allowed Values:	array
Default Value:	array()

Other settings: Alphabetical | By Function

[edit] Details

If a group can add any right (example: bureaucrats can add any right):

$wgAddGroups['bureaucrat'] = true;

If a group can add only some rights (example: bureaucrats can add only sysop and bot groups):

$wgAddGroups['bureaucrat'] = array( 'sysop', 'bot' );

MediaWiki version:

1.12

and after

Note that groups which may only grant some rights (like bureaucrats in this example) need to have set userrights privilege to false, otherwise they will still be able to add all groups (except in 1.11).