code: function () {
              /*  determine parameters  */
              var params = $cs.params("callable", arguments, {
                  name:  { pos: 0, req: true      },
                  value: { pos: 1, def: undefined }
              });
  
              /*  find service command  */
              var subscriptions = this._subscriptions(params.name);
              if (subscriptions.length !== 1)
                  return undefined;
              var cmd = subscriptions[0].func().command;
  
              /*  get or set "enabled" attribute  */
              return cmd.enabled(params.value);
          }
docs: /*  make a service callable (enable/disable it)