Check the basic opt:on features.

>>>>templates/test.tpl
<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<opt:root>
<div opt:on="true">With a tag</div>
<div opt:on="false">Without a tag</div>
</opt:root>

>>>>expected.txt
OUTPUT

>>>>result.txt
<div>With a tag</div>
Without a tag