common_can_character_create_trigger

common_can_character_create_trigger = {
	NOT = { has_truce = $FACTION_TARGET$ }
	common_character_validity_trigger = {
		FACTION_TARGET = $FACTION_TARGET$
	}
	trigger_if = {
		limit = {
			government_has_flag = government_has_house_blocs
			$FACTION_TARGET$ = top_liege
			is_confederation_member = yes
		}
		custom_tooltip = {
			text = is_house_head_of_noble_family_tt
			OR = {
				joined_faction ?= {
					any_faction_member = {
						OR = {
							this = root.house.house_confederation.leading_house.house_head
							is_ai = no
						}
					}
				}
				AND = {
					is_house_head = yes
					any_held_title = { is_noble_family_title = yes }
				}
				AND = {
					house.house_confederation.leading_house.house_head ?= {
						tgp_is_ceremonial_liege_trigger = yes
					}
					joined_faction.faction_leader ?= {
						is_leading_faction_type = restore_ceremonial_liege_faction
					}
				}
			}
		}
		custom_tooltip = {
			text = must_be_leading_house_of_bloc_trigger
			OR = {
				joined_faction ?= {
					any_faction_member = {
						OR = {
							this = root.house.house_confederation.leading_house.house_head
							is_ai = no
						}
					}
				}
				house.house_confederation.leading_house ?= house
				AND = {
					house.house_confederation.leading_house.house_head ?= {
						tgp_is_ceremonial_liege_trigger = yes
					}
					joined_faction.faction_leader ?= {
						is_leading_faction_type = restore_ceremonial_liege_faction
					}
				}
			}
		}
	}
	####
	# BLOCKERS
	####
	# General Faction immunity
	custom_description = {
		text = character_is_immune_to_factions
		subject = $FACTION_TARGET$
		NOT = { $FACTION_TARGET$ = { immune_to_factions_trigger = yes } }
	}
}

As written in game/common/scripted_triggers/00_faction_triggers.txt.