From always, Xpath has matched all elements with a given query, and I had to add [1] at the end to match only the first match.

In OpenERP 7 I have this view definition:

<record id="view" model="ir.ui.view">
    <field name="name">mail.message.full_expand</field>
    <field name="model">mail.message</field>
    <field name="inherit_id" ref="mail.view_message_form"/>
    <field name="arch" type="xml">
        <xpath expr="//field" position="attributes">
            <attribute name="readonly">1</attribute>
        </xpath>
    </field>
</record>

Its purpose is to copy another view, but fully read-only. However it stops at the first match. Is there any way to make Xpath match every field?