Menus serve as a syntax shortcut for a single-field forms with if-then-else sequence (switch) in its filled section. A <menu> element example:
<?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">
<menu>
<prompt>
Welcome home. Say one of: <enumerate/>
</prompt>
<choice next="http://www.sports.example.com/vxml/start.vxml">
Sports
</choice>
<choice next="http://www.weather.example.com/intro.vxml">
Weather
</choice>
<choice next="http://www.stargazer.example.com/voice/astronews.vxml">
Stargazer astrophysics news
</choice>
<noinput>Please say one of <enumerate/></noinput>
</menu>
</vxml>
(The example above was taken from W3C VoiceXML 2.0 CR specification document)
Fields can use <option> sub-elements to build simple grammars (lists of alternatives) in the same manner as menus while keeping <field> element semantics.