value will be an int or float.

        Subclasses may override this method.

def _set_topMargin(self, value):
        """
        value will be an int or float.

        Subclasses may override this method.
        """
        bounds = self.bounds
        if bounds is None:
            self.height = value
        else:
            xMin, yMin, xMax, yMax = bounds
            self.height = yMax + value