docs: def qteSetMark(self, markerID=0, line: int=None, col: int=None):
          """
          Define/overwrite the line- and column index of marker ``markerID``.
  
          The default marker has ``markerID=0`` by convention.
  
          If ``line`` and/or ``col`` are not provided they are substituted
          with the values of the current cursor position.
  
          ..note: ``line`` and ``col`` are not range checked. They can therefore
                  take on arbitrary values (even negative ones) that do not
                  denote a valid position in the document.
  
          |Args|
  
          * ``markerID`` (**object**): arbitrary Python object that is
            internally used as a dictionary.
          * ``line`` (**int**): an integer specifying the line
            number of the marker.
          * ``col`` (**int**): an integer specifying the column
            number of the marker.
  
          |Returns|
  
          * **None**
  
          |Raises|
  
          * **None**
          """
  
          # Query the line- and column number unless provided.
          if (line is None) and (col is None):
              line, col = self.getCursorPosition()
          elif line is None:
              line, _ = self.getCursorPosition()
          elif col is None:
              _, col = self.getCursorPosition()
          else:
              pass
  
          self.qteMarkers[markerID] = (line, col)
          return (line, col)