Checks, how opt:parent works.

>>>>templates/test.tpl
<opt:extend file="base.tpl">
<opt:snippet name="example">
<opt:parent />

</opt:snippet>
</opt:extend>

>>>>templates/base.tpl
<opt:root>
<opt:insert snippet="example">
<foo />
</opt:insert>
<opt:insert snippet="example" />
</opt:root>

>>>>data.php
$this->tpl->prologRequired = false;

>>>>expected.txt
OUTPUT

>>>>result.txt
<foo />