element nodes in a string?

I am a complete XML/XSLT newbie.  I have spent a lot
of time reading the FAQ and archives, but I can't find
an answer to my problem.

I have a well-formed XML document as follows:

<top>
<text>Each text field contains arbitrary text.  It
could also contain

paragraph breaks, _underscores_, and ~phrases
delimited by tildes~.
</text>
<text>Underscores and tildes are guaranteed to come in
pairs, or _not at all_ in a given text field.
</text>
</top>

What I want to do is to process each of these text
fields, underlining text between underscores,
italicizing text between tildes, and keeping paragraph
breaks as they are, and output them in html and
(later) rtf.

In addition I have a few other special characters
which are being replaced, such as two hyphens
converted to an em dash, tab characters converted to
HTML &nbsp; etc.

My approach is to chain together a bunch of calls to a
standard replace-substring template:

<!-- convert two hyphens into an em dash -->
<xsl:variable name='temp2'>
	<xsl:call-template name='replace-substring'>
		<xsl:with-param name='text' select='$temp1'/>
		<xsl:with-param name='from' select='$dash'/>
		<xsl:with-param name='to'>&#8212;</xsl:with-param>
	</xsl:call-template>
</xsl:variable>

<!-- convert tab characters into two &nbsp;'s -->
<xsl:variable name='temp3'>
	<xsl:call-template name='replace-substring'>
		<xsl:with-param name='text' select='$temp2'/>
		<xsl:with-param name='from' select='$tab'/>
		<xsl:with-param
name='to'>&#160;&#160;</xsl:with-param>
	</xsl:call-template>
</xsl:variable>

I then call a template which converts _underscored
text_ into <U>underscored text</U>.  This works just
fine.  I also have a similar template which converts
~text within tildes~ to <I>text within tildes</I>.  

The problem is that I can't do both of them.  When I
pass the output of the underline template into the
italicize template, the <U> and </U> are stripped out
and I am left with just the <I>...</I> tags.  

I think this is because my italicize template calls
substring-before and substring-after, and these string
functions convert their arguments to strings, which
effectively strips out whatever markup I have in
place.

How do I do what I want?  Here is my underline
template; the italicize is similar.


<xsl:template name='underline'>
  <xsl:param name='text'/>
  <xsl:param name='und-delim'/>
  <xsl:choose>
    <xsl:when test='contains($text, $und-delim)'>
      <xsl:variable name='pre'>
        <xsl:copy-of select='substring-before($text,
$und-delim)'/>
      </xsl:variable>
			
      <xsl:variable name='tempstr'>
        <xsl:copy-of select='substring-after($text,
$und-delim)'/>
      </xsl:variable>
			
      <xsl:variable name='underlined'>
        <xsl:copy-of
select='substring-before($tempstr, $und-delim)'/>
      </xsl:variable>
			
      <xsl:variable name='next'>
        <xsl:call-template name='underline'>
          <xsl:with-param name='text'
select='substring-after($tempstr, $und-delim)'/>
          <xsl:with-param name='und-delim'
select='$und-delim'/>
        </xsl:call-template>
      </xsl:variable>
			
      <xsl:copy-of select='$pre'/>
      <U>
      <xsl:copy-of select='$underlined'/>
      </U>
      <xsl:copy-of select='$next'/>
    </xsl:when>
    <xsl:otherwise>
      <xsl:copy-of select='$text'/>
    </xsl:otherwise>
  </xsl:choose>	
</xsl:template>

Thanks for any help,
Chris



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