Region-code enhanced, aka "RCE" and "REA", was a strange attempt to have region-coded DVDs blocked from being played in different regions, even if the user had a region-free DVD player.
The protection was only used on a few DVDs as the scheme was broken rather easily.
How the scheme worked was as follows:
The disc had its main content (the movie) in Region 1. However, the video also had a user-control-disabled video loop of a map showing the regions, coded as region 2, 3, 4, 5, and 6. If the disc was then played in a non-region 1 player, the movie would just revert to the map loop video, which was impossible to leave.
RCE was broken very easily thanks to a simple flaw in its design. Region-free players play discs by using the last region that worked with the previously viewed disc. Therefore, inserting a Region 1 DVD, watching a few seconds, and then removing and inserting the RCE disc would let the enhanced disc play with no issues.
If you somehow have a disc with RCE, it is also easily broken now by every company with a DeCSS product, like Slysoft, DVDFab, DVDShrink, and more.