<schema xmlns=“www.ascc.net/xml/schematron” >

<pattern name="Predefined values">
     <rule context="AAA">
          <report test="normalize-space(.) = 'aaa' or normalize-space(.) = 'bbb'">O.K.</report>
          <assert test="normalize-space(.) = 'aaa' or normalize-space(.) = 'bbb'">The AAA value is not permitted.</assert>
     </rule>
</pattern>

</schema>