How to use the CLM API to relate or attach documents together?

Hello.

I’m looking to be able to use the CLM API (for Docusign CLM), to programmatically “attach” one uploaded document to another.

The PUT/PATCH /Documents endpoints seem to “accept” a list of RelatedDocuments, but it does not seem to update the list.

For reference, in the UI this would be equivalent to pressing the “attach” button next to “Related Documents” and choosing another document and pressing “save’.