BEX

The BEX format is an extension standard for DeHackEd patches introduced by the Boom source port. The main advantages of the BEX format is the ability to give actions to frames that had no action in the original Doom EXE and strings are not limited in length to that of the original message, a limit imposed by the way DeHackEd originally patched the EXE. Bex introduced friendly mnemonics to help make changing a Things bits more intuitive and also allowed the user to specify a custom par time for their maps.

External link
The BEX format on Enjay's Dehacked information and tutorials