getDeepest

deepest.xpath

//*[not(*)][count(ancestor::node()) 
                  = 
                    max(//*[not(*)]/count(ancestor::node()))
                    ]

deepest.xslt

<xsl:for-each-group select="//title"
  group-by="count(ancestor::*)">
  <xsl:sort select="current-grouping-key()">
    <xsl:if test="position()=last()">
     <xsl:copy-of select="current-group()"/>
    </if>
  </sort>
</xsl:for-each-group>

deepest02.xpath

innermost(//*)[count(ancestor::node()) 
                  = 
                    max(//*[not(*)]/count(ancestor::node()))
                    ]

deepest03.xslt

<xsl:accumulator name="depth" initial-value="0, 0" as="xs:integer*">
      <xsl:accumulator-rule match="*" phase="start"
         select="
            let $myDepth := head($value) + 1
            return
               ($myDepth, max(($myDepth, tail($value))))"/>
      <xsl:accumulator-rule match="*" phase="end"
         select="
            head($value) - 1, tail($value)
            "/>
   </xsl:accumulator>

deepest04.xslt

<xsl:function name="re:find-spine" as="node()+">
		<xsl:param name="node" as="node()"/>
		<xsl:variable name="end1" select="re:find-deepest($node) => path()"/>
		<xsl:variable name="newTree" as="node()" select="$node => re:make-root($end1)"/>
		<xsl:variable name="end2" as="node()" select="re:find-deepest($newTree)"/>
		<xsl:sequence select="$end2/ancestor-or-self::*"/>
	</xsl:function>