module mod1 {

    prefix abc;

    namespace "urn:cesnet:mod1";

    grouping ssh {

        container ssh {

            leaf key { type string; }

            leaf user {

                type string {

                    pattern '[a-z0-9]';

                }

            }

            leaf is_valid {

                type boolean;

                default "false";

            }

        }

    }

    container server {

        uses ssh {

            refine ssh/ssh {        // unknown node

                description "test";

            }

        }

    }

}