Simple EPUB 3 validation with XProc

<?xml version="1.0" encoding="UTF-8"?>
<p:declare-step version="1.0"
    xmlns:p="http://www.w3.org/ns/xproc"
    xmlns:c="http://www.w3.org/ns/xproc-step"
    xmlns:cx="http://xmlcalabash.com/ns/extensions"
    xmlns:svrl="http://purl.oclc.org/dsdl/svrl">

    <p:option name="doc" required="true"/>

    <p:import href="http://xmlcalabash.com/extension/steps/library-1.0.xpl"/>

    <p:group name="relaxng-validation">
        <p:exec command="java" result-is-xml="false" wrap-result-lines="true">
            <p:with-option name="cwd" select="replace(resolve-uri('.',base-uri()),'^file:','')">
                <p:inline>
                    <doc/>
                </p:inline>
            </p:with-option>
            <p:with-option name="args"
                select="concat('-jar lib/jing.jar -c schemas/epub-nav-30.rnc ', $doc)"/>
            <p:input port="source">
                <p:empty/>
            </p:input>
        </p:exec>
        <p:for-each>
            <p:iteration-source select="//c:line"/>
            <cx:message>
                <p:with-option name="message" select="normalize-space(.)"/>
            </cx:message>
            <p:sink/>
        </p:for-each>
    </p:group>

    <p:group  name="schematron-validation">
        <p:load>
            <p:with-option name="href" select="$doc"/>
        </p:load>
        <p:validate-with-schematron name="validate-with-schematron" assert-valid="false">
            <p:input port="schema">
                <p:document href="schemas/epub-nav-30.sch"/>
            </p:input>
            <p:input port="parameters">
                <p:empty/>
            </p:input>
        </p:validate-with-schematron>
        <p:sink/>
        <p:for-each>
            <p:iteration-source select="//svrl:failed-assert">
                <p:pipe port="report" step="validate-with-schematron"/>
            </p:iteration-source>
            <cx:message>
                <p:with-option name="message"
                    select="concat('FAILURE: ',local-name(/*),': ',normalize-space(/*/svrl:text/text()))"
                />
            </cx:message>
            <p:sink/>
        </p:for-each>
    </p:group>
</p:declare-step>