refresh(changedTiddlers) {

    if (this.callbacks.length == 0) {
      return;
    }

    for (let tRef in changedTiddlers) {

      if (!this.callbacks[tRef]) {
        continue;
      }

      if (this.wiki.getTiddler(tRef)) {

        this.logger('debug', `Executing a callback for: ${tRef}`);
        this.callbacks[tRef].execute(tRef);

        // a continue prevents deleting the callback
        if (!this.callbacks.isDeleteOnCall) {
          continue;
        }
      }

      this.remove(tRef);
    }

  }
this method has to be implemented at the top of the refresh method.
It checks for changed tiddlers that have
registered callbacks. If `deleteOnCall` was specified during
registration of the callback, the callback will be deleted
automatically.