des-file format is the language which is used to describe the special levels for NetHack. It is compiled into a binary file by lev_comp. It is not a real programming language: there is no flow control, and the order in which different NetHack features are created is fixed. lev_comp will create a .lev-file for each MAZE and LEVEL definition in the file. These .lev-files will be loaded into NetHack to make the special levels. The .lev-files NetHack loads are actually defined in dungeon.def.