code: def __download(self, url, loaded_schemata, options):
          
          try:
              reader = DocumentReader(options)
              d = reader.open(url)
              root = d.root()
              root.set("url", url)
              return self.schema.instance(root, url, loaded_schemata, options)
          except TransportError:
              msg = "import schema (%s) at (%s), failed" % (self.ns[1], url)
              log.error("%s, %s", self.id, msg, exc_info=True)
              raise Exception(msg)
docs: Download the schema.