<sch:schema xmlns:sch="http://www.ascc.net/xml/schematron" >
     <sch:title>Selected e-mails</sch:title>
     <sch:pattern name="Check address">
          <sch:rule context="email">
               <sch:assert test="contains(.,'@')"> @ is missing in an email</sch:assert>
          </sch:rule>
     </sch:pattern>
</sch:schema>