xh:head>
        <xh:title>XForms Alert</xh:title>
        <xf:model>
            <xf:instance id="instance">
                <instance>
                    <node value="Foo" valid="1" readonly="0" required="1"/>
                    <node value="" valid="1" readonly="0" required="1"/>
                    <node value="" valid="1" readonly="0" required="0"/>
                </instance>
            </xf:instance>
            <xf:bind ref="/instance/node/@value" constraint="../@valid = 1" readonly="../@readonly