The following file:

#ASDF 1.0.0
#ASDF_STANDARD 1.6.0
%YAML 1.1
%TAG ! tag:stsci.edu:asdf/
--- !core/asdf-1.1.0
history:
  extensions:
    - extension_class: "asdf.extension._manifest.ManifestExtension"
      extension_uri: "asdf://asdf-format.org/core/extensions/core-1.6.0"
      manifest_software:
        name: "asdf_standard"
        version: "1.1.1"
      software:
        name: "asdf"
        version: "4.1.0"
...

is valid as the asdf-1.1.0 schema:
https://github.com/asdf-format/asdf-standard/blob/main/resources/stable/schemas/stsci.edu/asdf/core/asdf-1.1.0.yaml
doesn't require that the history/extensions items have a specific tag (even if we ignore asdf-format/asdf-standard#436). This can be seen by loading and validating the above file (example.asdf) via:

import asdf
asdf.schema.validate(asdf.util.load_yaml("example.asdf", tagged=True))

However if we try to load the file with asdf.open we encounter an error:

File ~/projects/src/asdf/asdf/_asdf.py:278, in AsdfFile._check_extensions(self, tree, strict)
    276 installed = None
    277 for ext in self._user_extensions + self._plugin_extensions:
--> 278     if (extension.extension_uri is not None and extension.extension_uri == ext.extension_uri) or (
    279         extension.extension_uri is None and extension.extension_class in ext.legacy_class_names
    280     ):
    281         installed = ext
    282         break

AttributeError: 'dict' object has no attribute 'extension_uri'

since the python library assumes the extension objects are tagged (and then deserialized to a custom object).

This might extend to other objects/tags in the standard which are linked to the asdf object schema (which uses refs) including:

• history_entry
• software (which is also referenced in history_entry)

The expectation here is that these are valid files and the python library shouldn't produce an error on loading.