anchor.diff:  {
   
     ###### interface
  -  
  +
     options = {
  -  
  +
       services.openssh = {
   
         enable = mkOption {
  
positive.code:         default = "";
          description = "Verbatim contents of <filename>sshd_config</filename>.";
        };
        
      };
  
    };
  
negative.code: 
          daemonType = "fork";
  
          exec =
            ''
              ${pkgs.openssh}/sbin/sshd -h /etc/ssh/ssh_host_dsa_key \
                -f ${pkgs.writeText "sshd_config" cfg.extraConfig}
  