WHAT’S IN THE . DOCUMENTREVISIONS –V100 FOLDER?

You should see that hidden folder at the top level of most volumes containing edited documents. It contains saved versions of those docs, in a database which references old versions, probably using hard links. Alongside it you’ll also see the .Spotlight–V100 containing Spotlight indexes for that volume. The versions database is locked, inaccessible, and shouldn’t be disturbed, or you could lose all those old doc versions. There’s no point in copying it when you’re making a copy of a volume, as those versions won’t transfer to another volume.