1<?xml version="1.0" encoding="UTF-8"?> 2<grammar xmlns="http://relaxng.org/ns/structure/1.0"> 3 <start> 4 <element> 5 <choice> 6 <name>c</name> 7 <choice> 8 <name>a</name> 9 <name>b</name> 10 </choice> 11 </choice> 12 <empty/> 13 </element> 14 </start> 15</grammar> 16