def METHOD_NAME(self, line, ns):
    """Collect all notes for a given order line."""
    # OrderLine/cbc:Note
    notes = line.xpath("cbc:Note", namespaces=ns)
    # OrderLine/LineItem/cbc:Note
    notes += line.xpath("cac:LineItem/cbc:Note", namespaces=ns)
    notes = [x.text for x in notes if x.text and x.text.strip()]
    return "\n".join(notes)