Game concept
Martial Custom
From the game's encyclopedia
Martial Custom is the Cultural Pillar that determines what genders can act as Commanders or Knights.
Some Traditions and Doctrines can modify these rules for certain Characters.
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.
Martial Custom is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Martial Custom is the Cultural Pillar that determines what genders can act as Commanders or Knights." It is part of Cultural Pillar. Patch 1.20.1.2, from game/common/game_concepts/00_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
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.