def defineOperator( self, operator, widget = -1 ):
        """
        Adds a new operator for this rule.  If widget is supplied as -1, then \
        a QLineEdit will be used by default.
        
        :param      operator | <str>
                    widget   | <subclass of QWidget> || None || -1
        """
        if ( widget == -1 ):
            widget = QLineEdit
            
        self._operators[nativestring(operator)] = widget