Comments

MPM wrote on 10/15/2007, 7:28 AM
I don't believe it's optional in the spec -- adhering to the specs OTOH is obviously optional for players.

Early on a few brave companies/studios tried to push the limits of the specs, and had all sorts of problems with players not handling them. IMHO from then on commercial DVDs have usually played it pretty safe. Examples of player design whims include CC pass-through, & behavior of NEXT/PREV buttons on the remote.
Rich Reilly wrote on 10/15/2007, 10:39 AM
I was in a store and saw variability within a brand.