http://www.optimsys.cz/support/examples/example03.php
<?xml version="1.0" encoding="UTF-8"?>
<vxml version="2.0" xmlns="http://www.w3.org/2001/vxml">
<meta name="description" content="using variables example"/>
<meta name="author" content="OptimSys, s.r.o., Czech Republic (http://www.optimsys.cz)"/>
<meta name="copyright" content="free for any purpose"/>
<var name="a" expr="1"/>
<form id="start">
<var name="b" expr="'hello'"/>
<block>
<prompt> Variable a has value: <value expr="a"/> </prompt>
<prompt> Let's try to evaluate a simple expression: a+1 = <value expr="a+1"/> </prompt>
<prompt> Variable b has value: <value expr="b"/> </prompt>
<prompt> Let's try string concatenation: b+' world' = <value expr="b+' world'"/> </prompt>
</block>
</form>
</vxml>