Here's the snippet of code that won't validate:
if (user_age > 15 && user_age < 91)
It gets the following errors:
XML Parsing Error: StartTag: invalid element name
and
XML Parsing Error: xmlParseEntityRef: no name
The first error is thrown for the "less than" and the second one is thrown twice, once for each ampersand.
Replacing the above signs with &
and <
validates fine, but of course it completely ruins the function.
Or you can protect the script from the xml validation like this:
<script type="text/javascript">
//<![CDATA[
if (user_age > 15 && user_age < 91) {
// do soemthing
}
//]]>
</script>