Mixed Initiative Dialogs

<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml"
  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="weather_info">
 <grammar src="cityandstate.grxml" type="application/srgs+xml"/>
 <initial name="start">
  <prompt>For what city and state would you like the weather?</prompt>
  <help>Please say the name of the city and
    state for which you would like a weather report.</help>
  <noinput count="1"> <reprompt/></noinput>
  <noinput count="2"> <reprompt/>
    <assign name="start" expr="true"/></noinput>
 </initial>
 <field name="state">
  <prompt>What state?</prompt>
  <help>Please speak the state for which you want the weather.</help>
 </field>
 <field name="city">
  <prompt>Please say the city in <value expr="state"/>
                for which you want the weather.</prompt>
  <help>Please speak the city for which you want the weather.</help>
  <filled><  !-- Most of our customers are in LA. -->
     <if cond="city == 'Los Angeles' &amp;&amp; state == undefined">
       <assign name="state" expr="'California'"/>
     </if>
  </filled>
 </field>
 <filled>
   <submit next="/servlet/weather" namelist="city state"/>
 <filled>
</form>
</vxml>

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