| <grammar xmlns="http://relaxng.org/ns/structure/1.0"> | |
| <start> | |
| <ref name="top"/> | |
| </start> | |
| <define name="empty"> | |
| <empty/> | |
| </define> | |
| <define name="top"> | |
| <element name="top"> | |
| <choice> | |
| <ref name="empty"/> | |
| <element name="a"> | |
| <text/> | |
| </element> | |
| </choice> | |
| </element> | |
| </define> | |
| </grammar> |