code: def default(self):
          
          return self.v2_list or self.oci_index or self.oci or self.v2 or self.v1
docs: Return the default manifest schema version.
  
          Depending on the docker version, <= 1.9, used to push
          the image to the registry, v2 schema may not be available.
          In such case, the v1 schema should be used when interacting
          with the registry. An OCI digest will only be present when
          the manifest was pushed as an OCI digest.