cx:version attribute apparently ignored

[simonegasperoni]

Hello,
I'm trying to validate using a step p:validate-with-xml-schema with XSD 1.1,
It seems to be supported by Calabash XML from the version 1.0.19:

• Added a cx:version attribute to the p:validate-with-xml-schema step so that you can request XSD 1.1.

It s not clear to me how to use cx:version, unfortunately I did not find any doc or example of use online. This is the related snippet

    <p:when test="/NOTICE[@type='index']">
      <p:validate-with-xml-schema cx:version="1.1">
        <p:input port="schema">
          <p:document href="https://raw.githubusercontent.com/op-cellar-git/eurlex-xml-format/master/new/index.xsd"/>
        </p:input>
      </p:validate-with-xml-schema>
    </p:when>

the compete XPL here: https://github.com/op-cellar-git/eurlex-xml-format/blob/master/new/xproc/procxsd11.xpl
This attribute seems to be completely ignored. Don not know why.
Thanks,
Simone