+ /** Set the permissions to the given flagset.
+ *
+ * This function sets S::set('perms') with a flagset represeting the combination of
+ * $perms and $is_admin.
+ *
+ * $perms is an abstract object representing the permissions.
+ * $is_admin is a boolean, true if the current user has site-administration rights.
+ */
+ abstract protected function makePerms($perms, $is_admin);