module mod3 {

    prefix abc;

    namespace "urn:cesnet:mod3";

    grouping ssh {

        container ssh {

            leaf key { type string; }

            leaf user {

                type string {

                    pattern '[a-z0-9]';

                }

            }

            leaf is_valid {

                type boolean;

                default "false";

            }

        }

        choice ch1 {

            case ca {

                container presence {

                    presence "enable";

                }

            }

            leaf str { type string; }

        }

    }

    container server {

        uses ssh {

            refine ch1 {

                description "test";

                default string;     // nothing case string

            }

        }

    }

}