<xsl:stylesheet exclude-result-prefixes="#all" 
   xmlns="tag:textalign.net,2015:ns"
   xmlns:xs="http://www.w3.org/2001/XMLSchema"
   xmlns:tan="tag:textalign.net,2015:ns"
   xmlns:array="http://www.w3.org/2005/xpath-functions/array"
   xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="3.0">

   <!-- TAN Function Library extended sequence functions. -->
   
   <xsl:function name="tan:most-common-item" as="item()?" visibility="public">
      <!-- Input: any sequence of items -->
      <!-- Output: the one item that appears most frequently -->
      <!-- If two or more items appear equally frequently, only the first is returned -->
      <!-- kw: sequences, items -->
      <xsl:param name="sequence" as="item()*"/>
      <xsl:for-each-group select="$sequence" group-by=".">
         <xsl:sort select="count(current-group())" order="descending"/>
         <xsl:if test="position() = 1">
            <xsl:copy-of select="current-group()[1]"/>
         </xsl:if>
      </xsl:for-each-group>
   </xsl:function>
   
   

</xsl:stylesheet>