'Return the style of *style_type* matching *style_id*. Returns the
default for *style_type* if *style_id* is not found or is |None|, or
if the style having *style_id* is not of *style_type*.'

def get_by_id(self, style_id, style_type):

    if (style_id is None):
        return self.default(style_type)
    return self._get_by_id(style_id, style_type)
