Parameter $group_type not documented in og_is_member()

Documentation for the $group_type parameter in the og_is_member() function is missing.

/**
 * Return TRUE if entity belongs to a group.
 *
 * @param $gid
 *   The group ID.
 * @param $entity_type
 *   The entity type.
 * @param $entity
 *   The entity object. If empty the current user will be used.
 * @param $states
 *   (optional) Array with the state to return. If empty groups of all state will
 *   return.
 *
 * @return
 *   TRUE if the entity (e.g. the user) belongs to a group and is not pending or
 *   blocked.
 */
function og_is_member($group_type, $gid, $entity_type = 'user', $entity = NULL, $states = array(OG_STATE_ACTIVE)) {
}