Support for multiple yaml document in one ASDF file

[ketozhang]

YAML spec supports having multiple files be combined into one using the --- separator to begin a document and optionally end one with .... I will call it multi-documents.

Is this feature currently supported by the ASDF spec? If so, are there any libraries that have implemented reading from multi-documents?

A use case for this is similar to tarball a set of files but I wish to preserve readability of the ASDF metadata by tools.

[braingram]

The current specification contains the following:

The tree must contain exactly one YAML document, starting with --- (YAML document start marker) and ending with ... (YAML document end marker), each on their own line.

There has been some discussion of expanding this for a 2.0.0 version of the file format: #487

[ketozhang]

Thank you @braingram!

[jsobeck]

Thanks, @braingram. As you might able to discern, (Roman) SSC is interested in this.

[braingram]

Thanks. FYI there is no plan for including this type of change in 2.0.0 and no timeline for a 2.0.0.

[ketozhang]

It makes sense, it's quite a significant change for client libraries as well. Feel free to close or keep open (+ attach to #487)

[braingram]

Thanks. Keeping it open sounds good to me. I attached it to #487