Game concept
Unique Game Rule
From the game's encyclopedia
This Game Rule significantly alters the gameplay experience.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Unique Game Rule is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "This Game Rule significantly alters the gameplay experience." Patch 1.20.1.2, from game/common/game_concepts/00_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
for a guide, post or blog
Source: game/common/game_concepts/00_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.