Page "Hexen: Beyond Heretic" Paragraph 6

Whereas Doom, Doom II, and Heretic rely on lines within the maps to perform simple actions, Hexen also allows these actions to be activated via Action Code Script ( ACS ).

These scripts use a syntactic variant of C, thus allowing special sequencing of game actions.

Programming features such as randomization, variables, and intermap script activation enable smooth hub gameplay and are responsible for most of the special effects within the game: On-screen messages ; random sound effect and monster spawning ; sidedef texture changes ; versatile control of polyobjects ; level initialization for deathmatch ; and even complex environment changes such as earthquakes manipulating floor levels and textures.