Manual:Skinning/Subtitle
Appearance
On certain pages (including this page!), a subtitle will appear under the title.
To modify the subtitle, extensions can use hooks to call the OutputPage::addSubtitle method.
$wgHooks['BeforePageDisplay'][] = function ( $out, $skin ) {
$out->addSubtitle( 'HELLO I AM A SUBTITLE' );
};
For modifying the subtitle that appears on sub pages, such as this page, you can use Manual:Hooks/SkinSubPageSubtitle.