Return the default style for *style_type* or |None| if no default is
        defined for that type (not common).

def default(self, style_type):
        """
        Return the default style for *style_type* or |None| if no default is
        defined for that type (not common).
        """
        style = self._element.default_for(style_type)
        if style is None:
            return None
        return StyleFactory(style)