form_siam_kingdom_decision_scripted_effect

form_siam_kingdom_decision_scripted_effect = {
	save_scope_as = founder
	create_title_and_vassal_change = {
		type = created
		save_scope_as = title_change
		add_claim_on_loss = no
	}
	title:k_siam = {
		change_title_holder = {
			holder = root
			change = scope:title_change
		}
	}
	resolve_title_and_vassal_change = scope:title_change
	add_prestige_experience = major_fame_gain

	hidden_effect = {
		title:k_siam = { save_scope_as = siam_kingdom }
		title:d_sukhothai = { save_scope_as = sukhotai_duchy }
		title:d_lop_buri = { save_scope_as = lop_buri }
		title:d_sukhothai = { set_de_jure_liege_title = title:k_siam }
		title:d_lop_buri = { set_de_jure_liege_title = title:k_siam }
		every_held_title = { # add other duchies if I hold any in the region
			limit = {
				tier = tier_duchy
				any_de_jure_county = {
					title_province = {
						OR = {
							geographical_region = world_asia_thailand
							geographical_region = world_asia_malaysia
						}
					}
				}
				NOT = {
					this = title:d_sukhothai
					this = title:d_lop_buri
				}
			}
			set_de_jure_liege_title = title:k_siam
		}
	}
	custom_tooltip = form_siam_kingdom_decision_effects_de_jure_tt_a
}

As written in game/common/scripted_effects/00_major_decisions_scripted_effects.txt.