add capability to a role to manage Membership

Hy

i want to add the capability to the role 'membership_manager' (for example ) with this function :

function add_theme_caps() {

$role = get_role('membership_manager');
$role->add_cap( '????????????' );
$role->add_cap('?????????');
etc ...
}

what's the name of the capability(ies) for Membership ?

Thank's