The Form*PYM.xsd schemas are meant to be a payment only option and used in conjunction with the following ReturnType enumerations:

Form540EX - Individual Resident extension payments
Form540BEX - Individual Nonresident extension payments
Form620EX - Corporate extension payments
Form541EX - Fiduciary extension payments
Form565EX - Partnership extension payments

In future years other payment types such as estimated payments will be allowed.