code: function () {
              /*  determine parameters  */
              var params = $cs.params("_subscription", arguments, {
                  id:      { pos: 0, req: true  },
                  details: { pos: 1, def: false }
              });
  
              /*  determine whether subscription exists  */
              var result = (typeof this.__subscription[params.id] !== "undefined");
  
              /*  optionally provide details about subscription  */
              if (params.details)
                  result = (result ? this.__subscription[params.id] : undefined);
  
              return result;
          }
docs: /*  determine subscription existence