5. What is regional code enhancement ?
Regional code enhancement (or RCE) is a mechanism to check for the default region setting of the DVD player and disallow playback if the default region is not the right one. This digital enhancement was initially added to some Warner Brothers and Columbia DVDs to stop region-1 DVDs from playing on "region-free" or "multi-region" DVD players.

An RCE disc has all its region flags set so that the player does not know which region is a valid one. The region verification process is performed by standard DVD virtual commands embedded on the disc program material. The verification process often begins at the beginning of each movie title or at the beginning of each chapter. The actual region code intended for the disc is compared against what is actually retrieved from a player. Depending upon the result, playback is directed to display a message or proceed normally.

Most RCE discs embeds the verification codes in many places of the disc to make the manual removal of RCE codes tedious or time intensive (not impossible). When an RCE disc detects a wrong region or an all-region player, it usually does not start the normal play back flow, and simply puts up a display of a world region map telling the viewer that the disc is incompatible with the player as following.

The good news is that most DVD backup software can automatically search for RCE-related instructions and make the appropriate changes for a selected region to render this protection scheme useless.