Structuring VoiceXML Using Sub-dialogs

<?xml version="1.0" encoding="UTF-8"?>
<vxml xmlns="http://www.w3.org/2001/vxml" version="2.0"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://www.w3.org/2001/vxml
   http://www.w3.org/TR/voicexml20/vxml.xsd">
  <form id="billing_adjustment">
    <var name="account_number"/>
    <var name="home_phone"/>
    <subdialog name="accountinfo" src="#basic">
      <filled>
        <assign name="account_number" expr="accountinfo.acctnum"/>
        <assign name="home_phone" expr="accountinfo.acctphone"/>
      </filled>
    </subdialog>
    <!-- the dialog continues here by manipulating the user's account -->
    ...
  </form>

  <!-- the subdialog (can reside a different VoiceXML document) -->
  <form id="basic">
    <field name="acctnum">
      <grammar type="application/srgs+xml" src="/grammars/digits.grxml"/>
      <prompt> What is your account number? </prompt>
    </field>
    <field name="acctphone">
      <grammar type="application/srgs+xml" src="/grammars/phone_numbers.grxml"/>
      <prompt> What is your home telephone number? </prompt>
      <filled>
        <return namelist="acctnum acctphone"/>
      </filled>
    </field>
  </form>
</vxml>

(The example above was adapted from W3C VoiceXML 2.0 CR specification document)