Check if adding the appropriate xmns to opt:root does not
crash anything.

>>>>templates/test.tpl
<?xml version="1.0" ?>
<opt:root xmlns:opt="http://xml.invenzzia.org/opt">
<foo>
Text &lt; foo &gt;
</foo>
</opt:root>

>>>>expected.txt
OUTPUT

>>>>result.txt
<foo>
Text &lt; foo &gt;
</foo>