Variable Substitution - How do I use a segment atribute ?

Hi all, I'm facing a problem with variable substitution in receiver comunication channel.

I got the follow message:

<?xml version="1.0" encoding="UTF-8"?>
<lote nro="000262007">
    <etc>...</etc>
</lote>

I want to get atribute <b>nro</b> from segment lote to use in variable substitution, how can I do it?