docs: def isSelectionPositionValid(self, selPos: tuple):
          """
          Return **True** if the start- and end position denote valid
          positions within the document.
  
          |Args|
  
          * ``selPos`` (**tuple**): tuple with four integers.
  
          |Returns|
  
          **bool**: **True** if the positions are valid; **False** otherwise.
  
          |Raises|
  
          * **None**
          """
          if selPos is None:
              return False
          if len(selPos) != 4:
              return False
          check1 = self.isPositionValid(*selPos[:2])
          check2 = self.isPositionValid(*selPos[2:])
          if check1 and check2:
              return True
          else:
              return False