code: public void insert(Widget widget, String tabText, int beforeIndex) {
          insert(widget, tabText, false, beforeIndex);
      }
docs: Inserts a widget into the tab panel. If the Widget is already attached to
  the TabPanel, it will be moved to the requested index.
  
  @param widget the widget to be inserted
  @param tabText the text to be shown on its tab
  @param beforeIndex the index before which it will be inserted