Mobile X+V 1.2

1.1 Motivation And Applications

XHTML 1.1 [XHTML 1.1] and XML Events [XML Events] are integrated using [XHTML Modularization] to enable interaction with VoiceXML 2.0 [VoiceXML 2.0] speech dialogs and thereby bring spoken interaction to the mobile web. The design leverages open industry APIs like the W3C DOM to create interoperable web content that can be deployed across a variety of end-user devices. Mobile X+V also enables the deployment of network-based voice services that can also be accessed from resource-limited thin clients to perform advanced multimodal functions.

Today, mobile web applications are authored in XHTML Basic [XHTML Basic] with user interaction created via XHTML form elements. The W3C is presently working on XForms [XForms], the next generation of web forms that bring the power of XML to web application development. The combination of XHTML and Voice described in this document can leverage the semantic richness of web applications created using XForms, while providing a smooth transition for today's developers wishing to deploy multimodal applications by adding spoken interaction to present-day web content. Integrating the work of the W3C voice browser working group into mainstream XHTML content has the advantage of ensuring that future enhancements to the voice browser component such as natural language understanding will be incorporated. This provides a smooth transition path for mobile web developers wishing to deliver increasingly smart user interaction for their web applications; further, the ability to use standardized voice technologies enables mobile service providers to deploy advanced voice solutions on the network that provide added value.

1.2 Differences between Mobile X+V and XHTML+Voice Profile 1.2

• The <xv:sync> html-form-id attribute is required (Sync).

• JavaScript variables or input controls defined within the XHTML container cannot be accessed within VoiceXML forms. For example, the VoiceXML <assign> element cannot be used to update an HTML control. However, the VoiceXML standard application variables are still available on the client (Accessing Speech Dialog Results from XHTML).

• VoiceXML forms cannot be embedded within an XHTML document. The external VoiceXML forms are referenced within a Mobile X+V document with the XML Events handler attribute. Each external reference must contain a fragment identifer specifying the VoiceXML form ID appended to the absolute or relative URI (Processing Within One Document).

• The external VoiceXML forms referenced by a Mobile X+V document must be placed in a VoiceXML 2.0 document (e.g., root element is <vxml>). The VoiceXML 2.0 document must include an XML processing instruction that identifies its VoiceXML forms as Mobile X+V VoiceXML forms (VoiceXML Container for X+V).

• Document linking with voice is neither required nor disallowed by the X+V 1.0 mobile profile (Document Linking with Voice).

• An X+V Mobile Profile user agent does not need to keep the document dynamically updated. If the document is updated after it is loaded, for example by modifying the DOM through dynamic HTML, the text referenced by a VoiceXML <prompt> src attribute may not be updated (Dynamic Prompt Generation in XHTML).

• The location of a VoiceXML document can be specified using the XHTML <link> element (Specifying External VoiceXML Documents).

• XHTML+Voice namespace prefixing is removed from the <sync> element's attributes, input, field, and html-form-id (Sync).

• The voice-handler attribute is removed from the <cancel> element (Cancel).

• The scope attribute on a VoiceXML <form> element is supported by Mobile X+V (VoiceXML Dialog Activation).

1.3 Design Principles

Mobile X+V is an XML application [XML 1.0].

1. XHTML is the host language.
2. Mobile X+V extends XHTML Basic [XHTML Basic] with an appropriate mobile subset of VoiceXML 2.0, as well as XML-Events.
3. Mobile X+V makes authoring easy for common types of multimodal interactions.
4. VoiceXML modularization is used to create a mobile profile that meets the needs of mobile clients with limited resources.
5. VoiceXML modularization does not alter the VoiceXML execution model. Specifically, a speech dialog is run as specified by the VoiceXML form interpretation algorithm. This enables mobile devices to rely on network-based voice services built on the VoiceXML platform.
6. VoiceXML modularization does not modify the function of the VoiceXML 2.0 elements and attributes that are part of the profile.

1.4 Mobile X+V Processing Model

Mobile X+V is designed for creating multimodal dialogs that combine in a straightforward way the visual input mode represented by XHTML and speech input and output as represented by VoiceXML. Here is a "Hello World" example of Mobile X+V.

<?xml version="1.0"?>
<html 
xmlns="http://www.w3.org/1999/xhtml"
xmlns:ev="http://www.w3.org/2001/xml-events"
xmlns:xv="http://www.voicexml.org/2002/xhtml+voice" >
  <head>
    <title>Hello World!</title>
  </head>
  <body>
    <h1>X+V Example</h1>
    <p ev:event="click" ev:handler="helloworld.vxml#sayHello">
      Hello World!
    </p>
  </body>
</html>

<?xml version="1.0" encoding="UTF-8"?>
<?xv version="1.2"?> 
<vxml 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.voicexml.org/specs/multimodal/x+v/mobile/12/schema/vxml.xsd"
  xmlns:xv="http://www.voicexml.org/2002/xhtml+voice"
  version="2.0">
  <!-- voice handler -->
  <form id="sayHello">
    <block>Hello World!</block>
  </form>
</vxml>

The speech dialog identified by "sayHello" is activated when the user clicks anywhere on the paragraph identified by "hello." The speech dialog is a VoiceXML form that synthesizes the text obtained from the same paragraph that activated the form. The speech output is "Hello World!"

When deploying to mobile devices, the voice functions may reside either on the device, or on the network; Mobile X+V permits both forms of deployment, thereby enabling mobile service providers to create value-add voice services that run on the network and are accessed by resource-limited clients.

<?xml version="1.0"?> 
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:ev="http://www.w3.org/2001/xml-events"
      xmlns:xv="http://www.voicexml.org/2002/xhtml+voice" >
   <head><title>Find City or Airport</title>
      <link rel="voicexml" type="application/voicexml+xml" href="cityorairport.vxml"/> 

      <xv:sync input="city" field="cityorairport.vxml#cityorairport"
			html-form-id="xform" />      

   </head>
   <body bgcolor="#FFFFFF">
      <h3>City or Airport</h3>
      <form id="xform" action="cgi/cityorairport.jsp">
         <p id="cityorairportprompt">Enter city or airport:</br>
            <input type="text" name="city"
                     ev:event="focus" ev:handler="cityorairport.vxml#vform"/>
         </p>
      </form>
   </body>
</html>

<?xml version="1.0" encoding="UTF-8"?>
<?xv version="1.2"?>
<vxml 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.voicexml.org/specs/multimodal/x+v/mobile/12/schema/vxml.xsd"
  xmlns:xv="http://www.voicexml.org/2002/xhtml+voice"
  version="2.0">

      <!-- voice handler -->
      <form id="vform">
         <field name="cityorairport" xv:id="cityorairport">
            <grammar src="cityorairport.grxml"/>
            <prompt src="cityorairport.html#cityorairportprompt"/> 
            <catch event="error.badfetch">
               Error fetching grammar!
               <return/>
            </catch>
         </field> 
      </form>

</vxml>

<?xml version="1.0"?>
<html  xmlns="http://www.w3.org/1999/xhtml" 
       xmlns:ev="http://www.w3.org/2001/xml-events"
       xmlns:xv="http://www.voicexml.org/2002/xhtml+voice">
  <head><title>XML Events Example</title>

    <script>
           var isDocumentLoaded = false;
    </script>

    <script id="scr1" declare="declare">
       if (isDocumentLoaded) {
	   alert("Please say yes or no");
       }

       isDocumentLoaded = true;
    </script>

    <ev:listener ev:observer="ex1" ev:event="vxmlnoinput" ev:handler="#scr1"/>
    <ev:listener ev:observer="ex1" ev:event="foo.bar"
        ev:handler="eventexample.vxml#vform2"/>

    <xv:sync input="button" field="eventexample.vxml#fld1" html-form-id="fo1"/>

  </head>
  <body id="bd1" ev:event="load" ev:handler="eventexample.vxml#vform1">
     <form id="fo1" action="http://www.example.com/x+v/cgi/example.pl">
         <input name="button" type="radio" value="yes"/>
         <input name="button" type="radio" value="no"/>
     </form>
  </body>
</html>

<?xml version="1.0" encoding="UTF-8"?>
<?xv version="1.2"?>
<vxml 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.voicexml.org/specs/multimodal/x+v/mobile/12/schema/vxml.xsd"
  xmlns:xv="http://www.voicexml.org/2002/xhtml+voice"
  version="2.0">

  <!-- voice handlers -->
  <form id="vform1">
     <catch event="noinput">
       <throw event="foo.bar"/>
     </catch>
     <field name="fld1" xv:id="fld1">
        <grammar type="boolean"/>
        <prompt>Say yes or no</prompt>
     </field>
  </form>

  <form id="vform2">
     <block>
       Foo bar event received.
     </block>
  </form>

</vxml>

<p id="warnPara" class="warn">warning</p>

1.5 Accessibility and Mobile X+V

This section is TBD.

2.1 Modularization of VoiceXML 2.0

2.2 Speech Dialogs

Modules vxml-exec-1.xsd, vxml-filled-1.xsd, vxml-resource-1.xsd, vxml-flow-1.xsd, vxml-enumerate-1.xsd, vxml-option-1.xsd, and vxml-form-1.xsd support authoring handlers that implement speech dialogs.

2.3 Executable Content

Modules vxml-filled-1.xsd, vxml-flow-1.xsd, vxml-exec-1.xsd, and vxml-resource-1.xsd declare constructs for use within voice handlers. The semantics of these constructs are as defined in the VoiceXML 2.0 specification.

2.4 Speech Grammars

The speech grammar modules provide constructs for authoring speech grammars as specified in VoiceXML 2.0. The modules are provided by the normative VoiceXML 2.0 SCHEMA and are unchanged: grammar-core.xsd, grammar.xsd, vxml-grammar-restriction.xsd, and vxml-grammar-extension.xsd. The restriction and extension modules allow the elements and attributes normatively specified by the speech grammar specification [Speech Grammars] to be included within the VoiceXML 2.0 namespace.

2.5 Speech And Non-speech Audio Output

The speech and audio output modules define constructs for producing spoken and non-spoken audio output. The modules are provided by the normative VoiceXML SCHEMA and are unchanged: synthesis-core.xsd, synthesis.xsd, vxml-synthesis-restriction.xsd, and vxml-synthesis-extension.xsd. As with the speech grammar modules, the elements and attributes normatively defined in the SSML specification [SSML 1.0] are included within the VoiceXML 2.0 namespace.

2.6 Event Handling

Module vxml-events-1.xsd declares the event types defined in VoiceXML 2.0.

2.7 Script

Module vxml-script-1.xsd declares the <script> and <var> elements for ECMAScript support in the VoiceXML container. The <script> element is not allowed below the VoiceXML <form> element.

ECMAScript functions and variables can be accessed by voice handlers by declaring <script> and <var> elements below the VoiceXML container's <vxml> root element. However, global variables are initialized each time a voice handler is activated, which prevents data from being shared between voice handlers in the same container.

2.8 VoiceXML Container for X+V

Module vxml-root-1.xsd declares the root <vxml> document element and child elements <meta and <metadata>. The <meta> and <metadata< elements may be also be declared below the <grammar> and <prompt> elements.

<vxml 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.voicexml.org/specs/multimodal/x+v/mobile/12/schema/vxml.xsd"
      xmlns:xv="http://www.voicexml.org/2002/xhtml+voice">

3.1 Document Conformance

A conforming Mobile X+V document is a document that requires only the facilities described as mandatory in this specification. Such a document must meet all of the following criteria:

1. It must validate against the XML Schema found in the appendix of this document.

2. The root element of the document must be html.

3. The name of the default namespace on the root element must be the XHTML namespace name: http://www.w3.org/1999/xhtml.

3.2 User Agent Conformance

The user agent must conform to the "User Agent Conformance" section of the XHTML Basic specification [XHTML Basic], section 3.2.

The user agent must conform to the following additional user agent rule:

1. When the user agent claims to support facilities required by this specification through normative reference, it must do so in ways consistent with the facilities' definition.

3.3 XHTML Namespace Integration

The default XML namespace of a Mobile X+V document is XHTML. Mobile X+V extends XHTML with XML-events and X+V extensions. The XML-events and X+V extension elements and attributes are included through additional namespace declarations:

<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:ev="http://www.w3.org/2001/xml-events"
      xmlns:xv="http://www.voicexml.org/2002/xhtml+voice">

The name of the unique prefix identifier for each namespace within the document, for example, ev for XML Events elements and attributes, is left to the document author's discretion.

3.4 Mobile X+V

The XHTML functionality in the Mobile X+V document type is based upon the XHTML modules defined in [XHTML Modularization]. The Mobile X+V profile includes the XHTML modules defined in [XHTML Basic], such as the basic XHTML forms and tables modules. Added to the XHTML Basic modules are the following modules:

• The XHTML scripting module.
• XML Events as defined by the XML Events module, [XML Events]. XML-events with VoiceXML event types and handlers allow the XHTML author to associate voice-interaction specific behaviors.
• An X+V Extension module for facilitating the authoring of the interaction between the visual and speech modules.

The notation, terms and document conventions used here are borrowed from [XHTML 1.1].

The profile includes the XHTML basic module defined in [XHTML Basic], the XHTML scripting module defined in [XHTML 1.1], the XML Event module defined in [XML Events], the X+V extension module, and the VoiceXML 2.0 modules as defined by the VoiceXML Profile.

4.1 Listener

X+V extends XHTML with the XML-Events <listener> element and its attributes. The <listener> attributes are added to XHTML elements primarily for activating voice handlers. The <listener> element and attributes belong to the XML-Events namespace:

xmlns:ev="http://www.w3.org/2001/xml-events"

4.2 Event Types

For a given XML language extended with XML Events, a set of event types must be specified independently of the [XML Events] module. The XML Event types supported by the Mobile X+V profile include all event types defined for [HTML 4.01] intrinsic events. VoiceXML handler activation is specified by including with an XHTML element one of these event types as an XML event and an ID reference to the VoiceXML form as an XML event handler.

The Mobile X+V profile supports the following VoiceXML 2.0 event types: nomatch, noinput, error, and help. These event types are emitted to the XHTML container as the following X+V event types: vxmlnomatch, vxmlnoinput, vxmlerror, and vxmlhelp, respectively. The VoiceXML exit and cancel event types are supported within the VoiceXML form but are not propagated to the visual browser. Event types defined by the author within VoiceXML, also known as application-defined event types, are also propagated to the visual browser. However, the VoiceXML <form> element does not support adding the XML-Events attributes.

An additional X+V event type, vxmldone, is supported. The vxmldone event is generated when the voice handler completes without an error and the VoiceXML <return> element is not run. However, the <return> element can explicitly return the vxmldone event.

The Mobile X+V profile extends the XHTML <script> element with XML Events. The <script> element doesn't generate any events of its own, so the observer attribute is required to specify observing an XML event on another node in the XHTML tree. The <script> element can observe any HTML 4.01 intrinsic event or VoiceXML event. Here is an example of how a <script> element can be a handler for a vxmldone event. The value of XHTML input "drink" is updated when the voice handler "fid" completes:

<?xml version="1.0"?>
<html xmlns="www.w3.org/1999/xhtml"
      xmlns:ev="http://www.w3.org/2001/xml-events"
      xmlns:vxml="http://www.w3.org/2001/vxml"
      xmlns:xv="http://www.voicexml.org/2002/xhtml+voice" >
  <head><title>Script Event Handler</title>

    <script type="text/javascript">
      var isDocumentLoaded = false;
    </script>

    <script type="text/javascript" 
      ev:event="vxmldone" ev:observer="drink" declare="declare">
      if (isDocumentLoaded) {
        document.xform.drink.value = application.lastresult$[0].utterance;
      }

      isDocumentLoaded = true;
    </script>

  </head>
  <body>
    <form name="xform" action="cgi/submit">
      <input type="text" id="drink"
        ev:event="focus" ev:handler="scripthandler.vxml#fid"/>
    </form>
  </body>
</html>

<?xml version="1.0" encoding="UTF-8"?>
<?xv version="1.2"?>
<vxml 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.voicexml.org/specs/multimodal/x+v/mobile/12/schema/vxml.xsd"
  xmlns:xv="http://www.voicexml.org/2002/xhtml+voice"
  version="2.0">

  <form id="fid">
    <field name="f1">
      <grammar src="drink.grxml"/>
      <prompt>Coffee, tea, or milk?</prompt>
    </field>
  </form>

</vxml>

Note that the "declare" attribute is necessary to prevent the <script> contents from being evaluated on document load. For backwards compatibility with older web browsers a JavaScript variable, such as isDocumentLoaded in the above example, should be used to prevent the document load evaluation.

The following table matches the X+V event types with the XHTML or VoiceXML elements that support them. When the <listener> event attribute is added to an XHTML element, it must specify a event type supported by the element in the right-hand column. Because the HTML 4.01 event types have been translated into XML-event types, the "on" prefix for these event types have been removed.

4.3 X+V Event Propagation

All XML-events in a mobile X+V document propagate within the XHTML tree. The following diagram shows the capture and bubbling phases of an XML-Event as it travels from the HTML root tag to the target input tag, and from the target input tag back to the HTML root. The flow of events shown could be in response to the user clicking on a text input control.

Flow of XML-Events in X+V

For an XML-event emitted from a VoiceXML form, the target of the event is the XHTML element that activated the VoiceXML form. This allows a listener to observe a VoiceXML event, such as vxmldone, on the XHTML form or body element, where the target is an input element contained by the form. Here is an example that shows how the vxmldone event can be observed on the XHTML body element.

<?xml version="1.0" encoding="iso-8859-1"?>
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:ev="http://www.w3.org/2001/xml-events"
      xmlns:vxml="http://www.w3.org/2001/vxml"
      xmlns:xv="http://www.voicexml.org/2002/xhtml+voice">
<head><title>Flight Information</title>

<script>
   var isDocumentLoaded = false;
</script>

<script id="selectFlight" ev:event="vxmldone" ev:observer="bodyelm" declare="declare">
   if (isDocumentLoaded) {
      alert("You entered "+document.getElementById('in1').value);
   }

   isDocumentLoaded = true;
</script>

<xv:sync input="in1" field="vxmldone.vxml#flightno" html-form-id="formelm"/>

</head>
<body id="bodyelm" ev:event="load" ev:handler="flightno.vxml#flightform">
  <form id="formelm" action="">
      <label id="flt-lbl">Please choose a flight:<br/>
        <input type="text" name="in1" id="in1'/>
    </label>
  </form>
</body>
</html>

<?xml version="1.0" encoding="UTF-8"?>
<?xv version="1.2"?>
<vxml 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.voicexml.org/specs/multimodal/x+v/mobile/12/schema/vxml.xsd"
  xmlns:xv="http://www.voicexml.org/2002/xhtml+voice"
  version="2.0">

<form id="flightform">
   <field name="flightno" xv:id="flightno">
    <prompt src="#flt-lbl"/>
    <grammar src="flightinfo.grxml" type="application/srgs+xml"/>  
    <catch event="help nomatch noinput">
       Say United 480, for example.
    </catch>
  </field>
</form>

</vxml>

5.1 Sync

The X+V <sync> element adds support for synchronization of data entered via either speech or visual input. It synchronizes the value property of an XHTML input control with a VoiceXML field, as follows:

1. Speech dialog results are returned to both the VoiceXML field and the XHTML <input> element. Speech results are returned to the XHTML <input> element after all filled processing has been performed.
2. Keyboard data entered into the <input> element updates both the VoiceXML field and the XHTML <input> element.
3. Keyboard data entered into the <input> element satisfies the guard condition on the VoiceXML field.
4. For an active VoiceXML form with multiple fields, if the user gives focus to the input field, the FIA is instructed to visit the referenced VoiceXML field as the next item. This includes the mixed initiative case.

Sync does not activate a voice handler. If the <sync> element has specified an XHTML input control but no VoiceXML form is currently active, nothing will happen. If an event and event handler are also specified, then when the user clicks on the input control the VoiceXML form is activated and the guard conditions of the VoiceXML form items are cleared. The XHTML input control is not cleared if data is already there.

Only changes made while a VoiceXML form is active are synchronized. An existing XHTML input value does not update the synchronized VoiceXML <field> when the VoiceXML form is activated.

The <sync> element attributes are:

All <sync> element attributes are required. The type of the input attribute is NMTOKEN. The type of the field attribute is URI. The URI must include a fragment identifier that references a VoiceXML <field> ID. If the <field> element is in an external file, then the fragment identifier is appended to the URI. The type of the html-form-id attribute is IDREF.

5.2 Cancel

The X+V <cancel> element allows a document author to cancel a running speech dialog. It is a stand-alone element with no content that can be referenced as an XML Events event handler.

The <cancel> element has one attribute:

The id attribute is required. The type of the id attribute is ID.

<?xml version="1.0" encoding="iso-8859-1"?>
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:ev="http://www.w3.org/2001/xml-events"
      xmlns:vxml="http://www.w3.org/2001/vxml"
      xmlns:xv="http://www.voicexml.org/2002/xhtml+voice">
<head><title>Cancel Example</title>

  <xv:sync field="example.vxml#fld1" input="in1" html-form-id="xform"/>
  <xv:sync field="example.vxml#fld2" input="in2" html-form-id="xform"/>

  <xv:cancel id="can1"/>

</head>
  <body id="bd1" ev:event="load" ev:handler="example.vxml#form1">
    <form id="xform" action=".">
      <input type="text" name="in1"/>&nbsp;&nbsp;
      <input type="text" name="in2"/><br/>
      <input type="reset" name="reset" ev:event="click" ev:handler="example.vxml#form1"/><br/>
      <input type="button" name="cancel" value="Cancel Voice" ev:event="click" ev:handler="#can1">
  </form>
  </body>
</html>

The example above shows how <cancel> can be used to cancel either a specific speech dialog or the currently running speech dialog. The reset button in the example cancels the speech dialog identified by "fid1." The "Cancel Voice" button cancels the currently running dialog because the handler attribute is omitted from the <cancel> element that is activated when the button is clicked.

5.3 VoiceXML Field ID Attribute

X+V adds an optional id attribute to the VoiceXML <field> element. The id attribute is used by the <sync> element's field attribute to uniquely specify a VoiceXML <field> element.

5.4 VoiceXML Prompt SRC and EXPR Attributes

X+V extends the VoiceXML <prompt> element with two attributes, src and expr. The src attribute allows for the specification of a text source for speech output in an external document. In addition, the source may be [SSML 1.0] or text styled according to the aural styling rules defined in [CSS2]. For example, a style sheet may have the following styling rules for the XHTML <p> element:

P.romeo { voice-family: male; volume: loud; pause-before: 20ms; }
P.juliet { voice-family: female; volume: soft; }

A voice handler can play two prompts from two different text sources in the document, as follows:

<?xml version="1.0"?>
<html xmlns="http://www.w3.org/1999/xhtml" 
      xmlns:ev="http://www.w3.org/2001/xml-events"
      xmlns:xv="http://www.voicexml.org/2002/xhtml+voice">
  <head>
    <title>Prompt src Example</title>
  </head>

  <body ev:event="load" ev:handler="promptsrc.vxml#sayHello">
    <p id="hello_romeo" class="juliet">
      Romeo, Romeo, where art thou?
    </p>
    <p id="hello_juliet" class="romeo">
      I am here.
    </p>
  </body>
</html>

<?xml version="1.0" encoding="UTF-8"?>
<?xv version="1.2"?>
<vxml 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.voicexml.org/specs/multimodal/x+v/mobile/12/schema/vxml.xsd"
  xmlns:xv="http://www.voicexml.org/2002/xhtml+voice"
   version="2.0">
  <form id="sayHello">
    <block><prompt xv:src="promptsrc.html#hello_romeo"/>
           <prompt xv:src="promptsrc.html#hello_juliet"/>
    </block>
  </form>
</vxml>

The first prompt plays a soft female voice. The second prompt plays a loud male voice after a 20 ms pause.

The expr attribute allows for the text source to be determined dynamically. The value of the expr attribute is an expression that evaluates to a URI with a fragment identifier. Both the URI referenced by src and the URI resolved by expr include a fragment identifier that references the id attribute of an XML element containing text for the prompt. The type of the src attribute is URI and the type of the expr attribute is CDATA. Exactly one of src or expr may be specified; if both are specified an error.badfetch event is thrown.

A voice handler can play a prompt from a text source determined dynamically by the expr attribute expression, as follows:

<?xml version="1.0"?>
<html xmlns="http://www.w3.org/1999/xhtml" 
      xmlns:ev="http://www.w3.org/2001/xml-events"
      xmlns:xv="http://www.voicexml.org/2002/xhtml+voice">
  <head>
    <title>Prompt expr Example</title>
  </head>

  <body ev:event="load" ev:handler="promptexpr.vxml#sayHello">
    <p id="hello_romeo" class="juliet">
      Romeo, Romeo, where art thou?
    </p>
    <p id="hello_juliet" class="romeo">
      I am here.
    </p>
  </body>
</html>

<?xml version="1.0" encoding="UTF-8"?>
<?xv version="1.2"?>
<vxml 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.voicexml.org/specs/multimodal/x+v/mobile/12/schema/vxml.xsd"
  xmlns:xv="http://www.voicexml.org/2002/xhtml+voice"
  version="2.0">

<form id="sayHello">
  <var name="count" expr="0"/>
  <block name="block_1">
     <prompt xv:expr="count == 0 ?
       'promptexpr.html#hello_romeo' : 'promptexpr.html#hello_juliet'"/>
     <assign name="count" expr="count+1"/>
     <assign name="block_1" expr="undefined"/>
  </block>
</form>

</vxml>