code: protected void setHistoryEnabled (boolean historyEnabled)
      {
          if (historyEnabled && _historyModel == null) {
              _historyModel = _scrollbar.getModel();
              _historyModel.addChangeListener(this);
              resetHistoryOffset();
  
              // out with the subtitles, we'll be displaying history
              clearGlyphs(_subtitles);
  
              // "scroll" down to the latest history entry
              updateHistBar(_history.size() - 1);
  
              // refigure our history
              figureCurrentHistory();
  
          } else if (!historyEnabled && _historyModel != null) {
              _historyModel.removeChangeListener(this);
              _historyModel = null;
  
              // out with the history, we'll be displaying subtitles
              clearGlyphs(_showingHistory);
          }
      }
docs: Configures us for display of chat history or not.