How can I replace certain characters with their escaped variants using XSLT? - 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="$vMapFun"/>
<xsl:with-param name="pStr" select="."/>
</xsl:call-template>
</xsl:template>
<xsl:template name="escape" match="strmap:*" mode="f:FXSL">
<xsl:param name="arg1"/>
<xsl:variable name="vspecChars">/|&{}##~\"</xsl:variable>
<xsl:variable name="vEscaping" select=
"substring('"', 1 div contains($vspecChars, $arg1))
"/>
<xsl:value-of select=
"concat($vEscaping, $arg1, $vEscaping)"/>
</xsl:template>
</xsl:stylesheet>
when this transformation is aplied on the provided XML document:
<para>This is a sample {a contrived one at that} ~ it serves no special purpose.</para>
the wanted, correct result is produced:
#PP
This is a sample "{"a contrived one at that"}" "~" it serves no special purpose.
II. With XSLT 1.0 recursive named template:
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="text"/>
<xsl:template match="/">
#PP
<xsl:call-template name="escape">
<xsl:with-param name="pStr" select="."/>
</xsl:call-template>
</xsl:template>
<xsl:template name="escape">
<xsl:param name="pStr" select="."/>
<xsl:param name="pspecChars">/|&{}##~\"</xsl:param>
<xsl:if test="string-length($pStr)">
<xsl:variable name="vchar1" select="substring($pStr,1,1)"/>
<xsl:variable name="vEscaping" select=
"substring('"', 1 div contains($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>