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<sch:schema xmlns:sch="http://purl.oclc.org/dsdl/schematron" 
     xml:lang="en" >
    <sch:title>Schema for Additional Constraints in Schematron</sch:title>
    <sch:ns prefix="sch" uri="http://purl.oclc.org/dsdl/schematron" />
    
    <sch:p>This schema supplies some constraints in addition to those
    given in the ISO RELAX NG Schema for Schematron. 
    </sch:p>
    
    <sch:pattern> 
        <sch:rule context="sch:active">
            <sch:assert 
                test="//sch:pattern[@id=current()/@pattern]">
            The pattern attribute of the active element shall match the 
            id attribute of a pattern.
            </sch:assert>
        </sch:rule>
    
        <sch:rule context="sch:pattern[@is-a]">
            <sch:assert 
                test="//sch:pattern[@abstract='true'][@id=current()/@is-a]">
            The is-a attribute of a pattern element shall match 
            the id attribute of an abstract pattern.
            </sch:assert>
        </sch:rule>

        <sch:rule context="sch:extends">
            <sch:assert 
                test="//sch:rule[@abstract='true'][@id=current()/@rule]">
            The rule attribute of an extends element shall match 
            the id attribute of an abstract rule.
            </sch:assert>
        </sch:rule>    
        
        
        <sch:rule context="sch:let">
            <sch:assert 
                test = "not(//sch:pattern
                    [@abstract='true']/sch:param[@name=current()/@name])">
            A variable name and an abstract pattern parameter should not
            use the same name.
            </sch:assert>
        </sch:rule>    
            
    </sch:pattern>
</sch:schema>