<?xml version="1.0" encoding="UTF-8"?>

<grammar 

  xmlns="http://relaxng.org/ns/structure/1.0"

  ns="http://utc.fr/nf29/S1">

 <start>

 <element name="book">

   <optional>

   <element name="info">

      <element name="title"><text/></element>

      <optional>

      <element name="author">

        <element name="email"><text/></element>

      </element>

      </optional>

    </element>

   </optional>

   <oneOrMore>

   <element name="part">

     <ref name="Title"/>

     <choice>

       <ref name="Text"></ref>

       <oneOrMore>

        <element name="chapter">

          <ref name="Title"/>

          <ref name="Text"></ref>

        </element>

      </oneOrMore>

    </choice>

  </element>

  </oneOrMore>

</element>

</start>

<define name="Title">

  <element name="title"><text/></element>

   <optional>

   <element name="subtitle"><text/></element>

   </optional>

</define>

<define name="Text">

    <oneOrMore>

    <element name="para"><text/></element>

    </oneOrMore>

</define>

</grammar>