Horde_Perms_Permission::addGroupPermission PHP Method

    public function addGroupPermission($groupId, $permission, $update = true)
    {
        if (empty($groupId)) {
            return;
        }
        if ($this->get('type') == 'matrix' && isset($this->data['groups'][$groupId])) {
            $this->data['groups'][$groupId] |= $permission;
        } else {
            $this->data['groups'][$groupId] = $permission;
        }
        if ($update) {
            $this->save();
        }
    }