ExtraData

ExtraData is a text mode lump type in Eternity, designed as a predecessor to UDMF. It allows extended definitions for map things, linedefs or sectors when the map itself is designed in the classic Doom format. The extended ExtraData object definitions can be used by placing specific thing types, linedef specials or sector types in the map, causing the corresponding records in ExtraData to override the specific objects. An ExtraData lump (custom-named by the user) is attached to the map via the EMAPINFO lump.

Features that require ExtraData's extensions include, among others, thing TIDs, parameterized linedef specials or various sector special effects (custom damage, terrain types).

The upcoming UDMF map format for Eternity will no longer have use of an attached ExtraData, because UDMF is designed to fill the same purpose of arbitrary developer extensibility. ExtraData is only relevant for maps edited in fixed-size binary formats such as classic Doom or classic Hexen.

For complete reference, see the Eternity documentation on ExtraData.