Flagging records that don't match a particular pattern

Hello - I am relatively new to xslt.  I was wondering how to flag
records that don't match a pattern.  I am going to be iterating
through about 8000 xml files in java transforming them from one xml to
another format required by a different company.  I know that I am
going to miss some of the patterns at first but was wondering if
there's a way to flag the files that don't match up and maybe write
them to a seperate directory.

For example in matching author tags (<AU>Slade, Grant^Riggins,
John</Au>) - could I do something in the xsl:otherwise part?:
  <xsl:template match="AU">
       <contrib contrib-type="author">
           <xsl:choose>
               <xsl:when test="contains(., '^')">
                   <xsl:for-each select="tokenize(.,'\^')">
                       <xsl:choose>
                           <xsl:when test="contains(.,',')">
                               <name>
                                   <surname>
                                       <xsl:value-of
select="substring-before(.,',')"/>
                                   </surname>
                                   <given-names>
                                       <xsl:value-of
select="substring-after(.,',')"/>
                                   </given-names>
                               </name>
                           </xsl:when>
                       </xsl:choose>
                   </xsl:for-each>
               </xsl:when>
               <xsl:otherwise>OUTPUT TO DIFFERENT DIRECTORY
HERE?</xsl:otherwise>
           </xsl:choose>
       </contrib>
   </xsl:template>