docs: void extensionVisited(Date date, Extension extension)
      {
          final Extension oldCurrentExtension = getCurrentExtension();
          final ExtensionHistoryEntry historyEntry;
  
          historyEntry = new ExtensionHistoryEntry(date, extension);
  
          synchronized (extensionHistory)
          {
              extensionHistory.add(historyEntry);
          }
  
          firePropertyChange(PROPERTY_CURRENT_EXTENSION, oldCurrentExtension, extension);
      }