Most people making Boom-compatible maps are familiar with the set of features that Boom added, which are extensively documented in BOOMREF.TXT: raised limits, extended linedef and sector types, and so on. However, I discovered yesterday that there's one feature not documented in there and I decided that a thread on Doomworld was a good place to inform people. I've also made a very silly WAD file to demonstrate the feature.   Extended Help Screens allow WAD authors to embed extra fullsc