[Question] Are snapshots mandatory for a viewpoint in BCF 2.1?

BCF 2.1 topic documentation says

> The folder **contains** the following files ...

Later, the Viewpoint section states that Snapshot is optional.

Can you clarify if the snapshot is mandatory or not?

I'm asking because a vendor outputs an error if my topics generated with IfcOpenShell don't have a snapshot.
It took me a lot of time to figure out that this was the issue since the tech support only told me to check the specification, which I thought I was following correctly.

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As a quick heads up, some of the test cases in the release_2_1 branch are not BCF 2.1 compliant since they use the "Viewpoint_.bcfv" and "Snapshot_.png" filenames instead of the "viewpoint.bcfv" and "snapshot.png".

Read the BCF 2.1 topic documentation and its Viewpoint section, then inspect the release_2_1 branch test cases using Viewpoint_.bcfv and Snapshot_.png. Confirm the intended snapshot requirement and filename rules, then update the documentation or tests so the specification and examples agree.

Written by the indexing model from the issue text.