xliff_core_2.1.sch: canDelete' attribute is set to 'no', but the corresponding element is missing in the sibling target.

Hello,

a file
<?xml version="1.0" encoding="utf-8"?>
<xliff xmlns:mda="urn:oasis:names:tc:xliff:metadata:2.0" xmlns="urn:oasis:names:tc:xliff:document:2.0" srcLang="en-US" version="2.0" >
    <file id="1">
        <group id="content">
            <unit id="1">
                <segment>
                    <source>some <pc  id="p1"  canDelete="no">sentence</pc></source>
                </segment>
            </unit>
        </group>
    </file>
</xliff>

passes XLIFF2.0 validation using Lynx.

When validated using xliff_core_2.1.sch (https://tools.oasis-open.org/version-control/browse/wsvn/xliff/trunk/xliff-21/schemas/xliff_core_2.1.sch) an error "canDelete' attribute is set to 'no', but the corresponding element is missing in the sibling target." is reported.

Maybe the rule should check whether sibling <target> is defined first.

Regards,

Jan