tryton/view/purchase_form.xml

<?xml version="1.0"?>
<!-- This file is part of Tryton.  The COPYRIGHT file at the top level of
this repository contains the full copyright notices and license terms. -->
<data>
    <xpath expr="/form/field[@name='reference']" position="after">
        <label name="customer"/>
        <field name="customer"/>
        <label name="delivery_address"/>
        <field name="delivery_address"/>
        <newline/>
    </xpath>
    <xpath expr="/form/notebook/page[@id='info']/field[@name='invoice_method']"
        position="after">
        <label name="drop_location"/>
        <field name="drop_location"/>
    </xpath>
    <xpath expr="//group[@id='links']" position="inside">
        <link icon="tryton-shipment-in" name="sale_supply_drop_shipment.act_purchase_drop_shipment_form"/>
    </xpath>
</data>