It's still done even within Schengen, e.g. last year I took an overnight train from Vienna to Amsterdam, a trip entirely within Schengen. German police boarded

It's still done even within Schengen, e.g. last year I took an overnight train from Vienna to Amsterdam, a trip entirely within Schengen. German police boarded the train at the first station in Germany and walked the train to check everyone's passport.