<?xml version="1.0" encoding="UTF-8"?>
<grammar ns="http://www.gexf.net/1.1" xmlns="http://relaxng.org/ns/structure/1.0">
  <!-- extension point -->
  <define name="node-content" combine="interleave">
    <optional>
      <element name="parents">
        <ref name="parents-content"/>
      </element>
    </optional>
  </define>
  <!-- new point -->
  <define name="parents-content">
    <zeroOrMore>
      <element name="parent">
        <ref name="parent-content"/>
      </element>
    </zeroOrMore>
  </define>
  <!-- new point -->
  <define name="parent-content">
    <attribute name="for">
      <ref name="id-type"/>
    </attribute>
  </define>
</grammar>
