<?xml version="1.0"?>
<data><field name="send_sms" position="after">
                    <field name="send_letter"/>
                </field>
                <field name="mail_template_id" position="attributes">
                    <attribute name="invisible">not send_email and not send_letter</attribute>
                </field>
                <field name="join_invoices" position="attributes">
                    <attribute name="invisible">not send_email and not send_letter</attribute>
                </field>
            </data>