docs: def addTab(self, tab):
          """
          Adds a new tab to this panel bar.
  
          :param      tab | <XViewPanelItem> || <str>
  
          :return     <int>
          """
          if not isinstance(tab, XViewPanelItem):
              tab = XViewPanelItem(tab, self)
              tab.setFixedHeight(self.height())
  
          index = len(self.items())
          self.layout().insertWidget(index, tab)
  
          self.setCurrentIndex(index)
          return tab