Linedefs may be assigned types in order to perform special effects. Doom includes a wide selection of linedef types used in its levels, which may also be reused by level authors. Hexen generalized the linedef types as action specials, which can be placed on linedefs, but also on things and used in ACS scripts. Heretic, Strife, Doom 64 and some source ports also add their own linedef types. Python code to generate and decode linedef type numbers is available. The Unofficial Doom Specs document has additional information about linedef types.