1<grammar xmlns="http://relaxng.org/ns/structure/1.0"> 2 3 <start> 4 <element name="addressBook"> 5 <zeroOrMore> 6 <element name="card"> 7 <ref name="cardContent"/> 8 </element> 9 </zeroOrMore> 10 </element> 11 </start> 12 13 <define name="cardContent"> 14 <element name="name"> 15 <text/> 16 </element> 17 <element name="email"> 18 <text/> 19 </element> 20 </define> 21 22</grammar> 23