Supported Source Node Object Types

According to the documentation...

"Source nodes represent the tables or views where raw data is queried to be processed by subsequent nodes. They are not manually editable other than to change their location or add a description."

However I don't see my external tables as available sources which I logically expect them to be, I don't want to have to put a table or a view on top of this object to be able to source from it.

This could of course be because I've done something wrong in the unnecessarily complex Snowflake security setup but it would be great if you could confirm exactly which table/view types are supported for use as source nodes please?

A quick update to the documentation would be hugely appreciated as well.

Cheers,
Paul.