docs: def qteAddMiniApplet(self, appletObj: QtmacsApplet):
          """
          Install ``appletObj`` as the mini applet in the window layout.
  
          At any given point there can ever only be one mini applet in
          the entire Qtmacs application, irrespective of how many
          windows are open.
  
          Note that this method does nothing if a custom mini applet is
          already active. Use ``qteKillMiniApplet`` to remove that one
          first before installing a new one.
  
          |Args|
  
          * ``appletObj`` (**QtmacsApplet**): the new mini applet.
  
          |Returns|
  
          * **bool**: if **True** the mini applet was installed
            successfully.
  
          |Raises|
  
          * **QtmacsArgumentError** if at least one argument has an invalid type.
          """
          # Do nothing if a custom mini applet has already been
          # installed.
          if self._qteMiniApplet is not None:
              msg = 'Cannot replace mini applet more than once.'
              self.qteLogger.warning(msg)
              return False
  
          # Arrange all registered widgets inside this applet
          # automatically if the mini applet object did not install its
          # own layout.
          if appletObj.layout() is None:
              appLayout = QtGui.QHBoxLayout()
              for handle in appletObj._qteAdmin.widgetList:
                  appLayout.addWidget(handle)
              appletObj.setLayout(appLayout)
  
          # Now that we have decided to install this mini applet, keep a
          # reference to it and set the mini applet flag in the
          # applet. This flag is necessary for some methods to separate
          # conventional applets from mini applets.
          appletObj._qteAdmin.isMiniApplet = True
          self._qteMiniApplet = appletObj
  
          # Shorthands.
          app = self._qteActiveApplet
          appWin = self.qteActiveWindow()
  
          # Remember which window and applet spawned this mini applet.
          self._qteMiniApplet._qteCallingApplet = app
          self._qteMiniApplet._qteCallingWindow = appWin
          del app
  
          # Add the mini applet to the applet registry, ie. for most
          # purposes the mini applet is treated like any other applet.
          self._qteAppletList.insert(0, self._qteMiniApplet)
  
          # Add the mini applet to the respective splitter in the window
          # layout and show it.
          appWin.qteLayoutSplitter.addWidget(self._qteMiniApplet)
          self._qteMiniApplet.show(True)
  
          # Give focus to first focusable widget in the mini applet
          # applet (if one exists)
          wid = self._qteMiniApplet.qteNextWidget(numSkip=0)
          self._qteMiniApplet.qteMakeWidgetActive(wid)
          self.qteMakeAppletActive(self._qteMiniApplet)
  
          # Mini applet was successfully installed.
          return True