'Return the id of the style of *style_type* corresponding to
*style_name*. Returns |None| if that style is the default style for
*style_type*. Raises |ValueError| if the named style is not found in
the document or does not match *style_type*.'

def _get_style_id_from_name(self, style_name, style_type):

    return self._get_style_id_from_style(self[style_name], style_type)
