<element name="addressBook" xmlns="http://relaxng.org/ns/structure/1.0"> <zeroOrMore> <element name="card"> <element name="name"> <text/> </element> <element name="email"> <text/> </element> <optional> <element name="note"> <externalRef href="inline.rng"/> </element> </optional> </element> </zeroOrMore> </element>