Invalid attribute field-readonly in axf:form-field

[raducoravu]

We received this feedback:
https://www.oxygenxml.com/forum/viewtopic.php?f=7&t=24267
about an XSL-FO file like this being considered invalid as it uses the "field-readonly" attribute in an axf:form-field :

    <fo:root xmlns:fo="http://www.w3.org/1999/XSL/Format"
        xmlns:axf="http://www.antennahouse.com/names/XSL/Extensions"
        xml:lang="en">
        <fo:layout-master-set>
            <fo:simple-page-master master-name="spm">
                <fo:region-body/>
            </fo:simple-page-master>
        </fo:layout-master-set>
        <fo:page-sequence master-reference="spm">
            <fo:flow flow-name="xsl-region-body">
                <fo:block>Hello, wo<axf:form-field
    field-type="text"
    field-name="dontwritehere"
    field-readonly="true"
    field-flags="Hidden"
    field-default-text="You can't write here!"/>rld.</fo:block>
            </fo:flow>
        </fo:page-sequence>
    </fo:root>

[raducoravu]

Thanks @tgraham-antenna