$ xmllint --relaxng src/lxml/isoschematron/resources/rng/iso-schematron.rng - <<EOF
<schema xmlns="http://purl.oclc.org/dsdl/schematron">
    <pattern id="OpenModel">
        <title>Open Model</title>
        <rule context="AAA">
            <assert test="BBB"> BBB element is not present</assert>
            <assert test="CCC"> CCC element is not present</assert>
        </rule>
    </pattern>
    <pattern id="ClosedModel">
        <title>Closed model"</title>
        <rule context="AAA">
            <assert test="BBB"> BBB element is not present</assert>
            <assert test="CCC"> CCC element is not present</assert>
            <assert test="count(BBB|CCC) = count (*)">There is an extra element</assert>
        </rule>
    </pattern>
</schema>
EOF

<?xml version="1.0"?>
<schema xmlns="http://purl.oclc.org/dsdl/schematron">
    <pattern id="OpenModel">
        <title>Open Model</title>
        <rule context="AAA">
            <assert test="BBB"> BBB element is not present</assert>
            <assert test="CCC"> CCC element is not present</assert>
        </rule>
    </pattern>
    <pattern id="ClosedModel">
        <title>Closed model"</title>
        <rule context="AAA">
            <assert test="BBB"> BBB element is not present</assert>
            <assert test="CCC"> CCC element is not present</assert>
            <assert test="count(BBB|CCC) = count (*)">There is an extra element</assert>
        </rule>
    </pattern>
</schema>
- validates

$ build/tmp/libxml2-2.9.9/xmllint --relaxng src/lxml/isoschematron/resources/rng/iso-schematron.rng - <<EOF
<schema xmlns="http://purl.oclc.org/dsdl/schematron">
    <pattern id="OpenModel">
        <title>Open Model</title>
        <rule context="AAA">
            <assert test="BBB"> BBB element is not present</assert>
            <assert test="CCC"> CCC element is not present</assert>
        </rule>
    </pattern>
    <pattern id="ClosedModel">
        <title>Closed model"</title>
        <rule context="AAA">
            <assert test="BBB"> BBB element is not present</assert>
            <assert test="CCC"> CCC element is not present</assert>
            <assert test="count(BBB|CCC) = count (*)">There is an extra element</assert>
        </rule>
    </pattern>
</schema>
EOF

<?xml version="1.0"?>
<schema xmlns="http://purl.oclc.org/dsdl/schematron">
    <pattern id="OpenModel">
        <title>Open Model</title>
        <rule context="AAA">
            <assert test="BBB"> BBB element is not present</assert>
            <assert test="CCC"> CCC element is not present</assert>
        </rule>
    </pattern>
    <pattern id="ClosedModel">
        <title>Closed model"</title>
        <rule context="AAA">
            <assert test="BBB"> BBB element is not present</assert>
            <assert test="CCC"> CCC element is not present</assert>
            <assert test="count(BBB|CCC) = count (*)">There is an extra element</assert>
        </rule>
    </pattern>
</schema>
-:3: element title: Relax-NG validity error : Expecting element p, got title
Relax-NG validity error : Extra element rule in interleave
-:4: element rule: Relax-NG validity error : Element pattern failed to validate content
-:10: element title: Relax-NG validity error : Expecting element p, got title
Relax-NG validity error : Extra element rule in interleave
-:11: element rule: Relax-NG validity error : Element pattern failed to validate content
-:9: element pattern: Relax-NG validity error : Expecting element p, got pattern
Relax-NG validity error : Extra element pattern in interleave
-:9: element pattern: Relax-NG validity error : Element schema failed to validate content
- fails to validate