<schema xmlns="http://www.ascc.net/xml/schematron" >
<pattern name="Number of characters in an abbreviation">
<rule context="BBB">
<report test="string-length(@bbb) < 2">There is not enough letters in the abbreviation</report>
<report test="string-length(@bbb) > 3">There is too much letters in the abbreviation</report>
</rule>
</pattern>
</schema>