How can I replace certain characters with their escaped variants using XSLT?

Question

I'm trying to develop an XSLT stylesheet which transforms a given DocBook document to a file which can be fed to the lout document formatting system (which then generates PostScript output).

Doing so requires that I replace a few characters in the text of DocBook elements because they have a special meaning to lout. In particular, the characters

/ | & { } # @ ~ \ "

need to be enclosed in double quotes (") so that lout treats them as ordinary characters.

For instance, a DocBook element like

<para>This is a sample {a contrived one at that} ~ it serves no special purpose.</para>

should be transformed to

@PP
This is a sample "{"a contrived one at that"}" "~" it serves no special purpose.

How can I do this with XSLT? I'm using xsltproc, so using XPath 2.0 functions is not an option but a number of EXSLT functions are available.

I tried using a recursive template which yields the substring up to a special character (e.g. {), then the escaped character sequence ("{") and then calls itself on the substring after the special character. However, I have a hard time making this work properly when trying to replace multiple characters, and one of them is used in the escaped sequence itself.

Answer 1

In particular, the characters

/ | & { } # @ ~ \ " 

need to be enclosed in double quotes (") so that lout treats them as ordinary characters.

I. This is most easily accomplished using the str-map template of FXSL:

<xsl:stylesheet version="1.0" 
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
 xmlns:f="http://fxsl.sf.net/"
 xmlns:strmap="strmap"
 exclude-result-prefixes="xsl f strmap">
   <xsl:import href="str-dvc-map.xsl"/>

   <xsl:output method="text"/>

   <strmap:strmap/>

   <xsl:template match="/">
     <xsl:variable name="vMapFun" select="document('')/*/strmap:*[1]"/>
     @PP
     <xsl:call-template name="str-map">
       <xsl:with-param name="pFun" select="$vMapFun"/>
       <xsl:with-param name="pStr" select="."/>
     </xsl:call-template>
   </xsl:template>

    <xsl:template name="escape" match="strmap:*" mode="f:FXSL">
      <xsl:param name="arg1"/>

      <xsl:variable name="vspecChars">/|&amp;{}#@~\"</xsl:variable>

      <xsl:variable name="vEscaping" select=
       "substring('&quot;', 1 div contains($vspecChars, $arg1))
       "/>

      <xsl:value-of select=
      "concat($vEscaping, $arg1, $vEscaping)"/>
    </xsl:template>

</xsl:stylesheet>

when this transformation is aplied on the provided XML document:

<para>This is a sample {a contrived one at that} ~ it serves no special purpose.</para>

the wanted, correct result is produced:

@PP This is a sample "{"a contrived one at that"}" "~" it serves no special purpose.

II. With XSLT 1.0 recursive named template:

<xsl:stylesheet version="1.0" 
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
   <xsl:output method="text"/>

   <xsl:template match="/">
     @PP
     <xsl:call-template name="escape">
       <xsl:with-param name="pStr" select="."/>
     </xsl:call-template>
   </xsl:template>

    <xsl:template name="escape">
     <xsl:param name="pStr" select="."/>
     <xsl:param name="pspecChars">/|&amp;{}#@~\"</xsl:param>

     <xsl:if test="string-length($pStr)">
         <xsl:variable name="vchar1" select="substring($pStr,1,1)"/>

          <xsl:variable name="vEscaping" select=
           "substring('&quot;', 1 div contains($pspecChars, $vchar1))
           "/>

          <xsl:value-of select=
          "concat($vEscaping, $vchar1, $vEscaping)"/>

          <xsl:call-template name="escape">
           <xsl:with-param name="pStr" select="substring($pStr,2)"/>
           <xsl:with-param name="pspecChars" select="$pspecChars"/>
          </xsl:call-template>
      </xsl:if>
    </xsl:template>
</xsl:stylesheet>