Can't seen to use insertBefore

[Horny Porno-thologist]

Hi all,
I'm trying to use insertBefore to create opening/closing tags in my XML,
but to no avail - it says something
like "parent node cannot be accessed".

Anyway, this is what I'm trying to do:

convert something like this:

<?xml= .... etc>
<Food>
<Yellow>Butter</Yellow>
<White>Marzipan</White>
</Food>

to:

<?xml= .... etc>
<Colored_Food>
<Food>
<Yellow>Butter</Yellow>
<White>Marzipan</White>
</Food>
</Colored_Food>

Help please!