Thread:Talk:ResourceLoader/RL, media=print and print-only style sheets/reply

The skins.modern module is a great example:

'skins.modern' => array(		'styles' => array( 'modern/main.css' => array( 'media' => 'screen' ), 'modern/print.css' => array( 'media' => 'print' ), ),		'remoteBasePath' => $GLOBALS['wgStylePath'],		'localBasePath' => $GLOBALS['wgStyleDirectory'],	),

The $GLOBALS stuff is part of how core modules are defined in resources/Resources.php, you can ignore that. The important part is the  part.