Return an XMLSchema instance loaded from the given url.
           url -- URL to dereference
           schema -- Optional XMLSchema instance.

def loadFromURL(self, url, schema=None):
        """Return an XMLSchema instance loaded from the given url.
           url -- URL to dereference
           schema -- Optional XMLSchema instance.
        """
        reader = self.__readerClass()
        if self.__base_url:
            url = basejoin(self.__base_url,url)

        reader.loadFromURL(url)
        schema = schema or XMLSchema()
        schema.setBaseUrl(url)
        schema.load(reader)
        self.__setIncludes(schema)
        self.__setImports(schema)
        return schema