is_appointment_valid_trigger

is_appointment_valid_trigger = {
	$TITLE$ = { save_temporary_scope_as = title_temp }
	$CANDIDATE$ = { save_temporary_scope_as = candidate_temp }
	$TOP_LIEGE$ = { save_temporary_scope_as = top_liege_temp }
	custom_tooltip = { # Capital should be never a valid appointment (go for higher title instead
		text = not_top_liege_capital_county_tt
		trigger_if = { # Candidates outside a landed realm have no capital county to clash with
			limit = { exists = scope:candidate_temp.top_liege.capital_county }
			NOT = { scope:title_temp ?= scope:candidate_temp.top_liege.capital_county }
		}
	}
	scope:candidate_temp = {
		trigger_if = {
			limit = {
				scope:top_liege_temp = { tgp_realm_has_ceremonial_liege_trigger = yes }
				tgp_is_in_ceremonial_house_trigger = yes
			}
			trigger_if = {
				limit = {
					scope:title_temp ?= { has_variable = administrative_ui_special_title }
				}
				custom_tooltip = {
					text = ceremonial_liege_only_heir_can_be_ruler_trigger
					tgp_is_ceremonial_liege_or_direct_heir_trigger = yes
				}
			}
			trigger_else = {
				custom_tooltip = {
					text = ceremonial_liege_cannot_be_governor_trigger
					tgp_is_ceremonial_liege_trigger = no
				}
			}
		}
		trigger_if = {
			limit = { exists = scope:title_temp }
			custom_tooltip = { # Has relevant law
				text = has_appointment_succession_tt
				$TITLE$ = {
					OR = {
						has_title_law_flag = appointment_type_succession
						holder ?= { has_realm_law_flag = appointment_type_succession }
					}
				}
			}
			custom_tooltip = {
				text = follows_other_title_appointment_tt
				$TITLE$.tier = $TITLE$.holder.primary_title.tier
			}
			trigger_if = {
				limit = {
					NOT = { top_liege.highest_held_title_tier = scope:title_temp.tier }
				}
				is_adult = yes
			}
			trigger_if = {
				limit = {
					any_held_title = { count >= 1 }
				}
				trigger_if = {
					limit = { government_has_flag = government_is_celestial }
					custom_tooltip = { # Only one province of highest rank
						text = cannot_compete_for_lower_rank_titles_tt
						NOT = {
							any_held_title = {
								tier > scope:title_temp.tier
								is_landless_type_title = no
								is_noble_family_title = no
							}
						}
					}
				}
				trigger_else = {
					custom_tooltip = { # Only one province of highest rank
						text = only_one_province_of_highest_rank_tt
						NOT = {
							any_held_title = {
								tier = scope:title_temp.tier
								is_landless_type_title = no
								is_noble_family_title = no
							}
						}
					}
				}
				custom_tooltip = {
					text = promote_candidate_interaction_existing_holder_tt
					this != scope:title_temp.holder
				}
			}
		}
		custom_tooltip = {
			text = can_be_appointed_interaction_tt
			OR = {
				can_be_granted_titles_by = { RULER = scope:top_liege_temp }
				can_be_granted_theocratic_titles_by = { RULER = scope:top_liege_temp }
				AND = {
					is_diarch_of_target = scope:top_liege_temp
					scope:top_liege_temp = { has_diarchy_active_parameter = diarchy_is_co_rulership }
				}
			}
		}
		custom_tooltip = { # Only administrative
			text = only_administrative_tt
			trigger_if = {
				limit = { is_landed = yes }
				government_has_mechanic = administrative
			}
		}
		is_clergy = no
	}
}

As written in game/common/scripted_triggers/07_ep3_triggers.txt.