is_available

is_available = {
	is_available_quick = {
		alive = yes
		travel = no
		in_army = no
		imprisoned = no
		incapable = no
	}
	has_contagious_deadly_disease_trigger = no
	custom_description = {
		text = ALREADY_IN_ACTIVITY
		NOR = {
			exists = involved_activity
			has_variable = {
				name = homage_liege_scope
				name = meditation_character_flag
				name = local_shrine_rite
				name = petition_liege_character_flag
				name = petition_head_of_faith_petitioner
				name = holding_court_character_flag
				name = gone_adventuring
			}
			is_being_visited_on_tour_strict = yes
		}
	}
	custom_description = {
		text = ALREADY_PLANNING_ACTIVITY
		NOT = { has_character_flag = planning_an_activity }
	}
	# Variable set on Mandala succession
	custom_tooltip = {
		text = busy_in_mandala_succession
		NOT = { has_variable = busy_in_mandala_succession }
	}
}

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