code: def addLineWidget( self, query = None ):
          
          widget = XQueryLineWidget(self)
          widget.setTerms(sorted(self._rules.keys()))
          widget.setQuery(query)
          
          index = self._container.layout().count() - 1
          self._container.layout().insertWidget(index, widget)
          
          widget.addRequested.connect(     self.addLineWidget )
          widget.removeRequested.connect(  self.removeLineWidget )
          
          # update the remove enabled options for these widgets
          self.updateRemoveEnabled()
docs: Adds a new line widget to the system with the given values.
          
          :param      query | (<str> term, <str> operator, <str> vlaue) || None