[xsl] markup.xsl stylesheet question

[M C <mcundiff11@xxxxxxxxx>]

I am trying the stylesheet by Jeni Tennison at: http://jenitennison.com/xslt/utilities/markup.xsl

This stylesheet is exactly what I need (i.e. to insert markup around a list of specified phrases that occur in the text nodes of an existing xml doc).

I am looking at the example page at:
http://jenitennison.com/xslt/utilities/markup-example.xml

and am wondering why (in the output) the final occurrence of the phrase "result tree" does not get marked up. Can anyone explain? Here is output (notice that the final occurrence of "result tree" is not wrapped in <em> tag as are the others.

Thanks,
Morgan
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<p>
  A <em>transformation</em> expressed in <em>XSLT</em> describes rules for transforming a <em>source tree</em> into
  a <em>result tree</em>. The <em>transformation</em> is achieved by associating patterns with templates. A
  pattern is matched against elements in the <em>source tree</em>. A <em>template</em> is instantiated to
  create part of the <em>result tree</em>. The <em>result tree</em> is separate from the <em>source tree</em>. The
  structure of the <em>result tree</em> can be completely different from the structure of the source
  tree. In constructing the result tree, elements from the <em>source tree</em> can be filtered and
  reordered, and arbitrary structure can be added.
</p>
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