Calabash and p:validate-with-xml-schema

Has Calabash implemented this step yet?  I know it's optional, so maybe it's
not high on the priority list.

I ask, because this XPL:

<p:declare-step xmlns:p="http://www.w3.org/ns/xproc">
    <p:input port="source">
        <p:document href="BookStore.xml"/>
    </p:input>
    <p:output port="result"/>
    <p:validate-with-xml-schema mode="lax">
        <p:input port="schema">
            <p:document href="BookStore.xsd"/>
        </p:input>
    </p:validate-with-xml-schema>
</p:declare-step>

gives a java.lang.NullPointerException with Calabash 0.6.0.  Maybe there's
an error in my pipeline?

Appreciate any help!

James Garriss
http://garriss.blogspot.com