Zsolt Szabó wrote:
Maybe I have found a solution. It works, at least with libxslt.
is this correct? I think is is rather a hack.
Didn't my solution work? I think your templates are correct but I'm not 
sure if they will produce correct results for paragraphs with 3 words or 
less. Also, I have the impression that they will only display the first 
3 words and skip the rest?
<!--Select the first paragraph of all chapters-->
<xsl:template match="//chapter/section[1]/para[1]" priority="1">
    <xsl:call-template name="first_line">
        <xsl:with-param name="string" select="."/>
    </xsl:call-template>
</xsl:template>
<!--Select all other paragraphs-->
<xsl:template match="//para">
    <xsl:call-template name="para.template">
    </xsl:call-template>
</xsl:template>
<xsl:template name="first_line">
    <xsl:param name="string"/>
    <xsl:param name="string2"/>
    <xsl:param name="string3"/>
        <xsl:choose>
       
            <!--are there any spaces???-->
            <xsl:when test="contains($string, ' ')">
                <div>
                    <b>
                        <!--1st word-->
                        <xsl:value-of 
select="substring-before($string,' ')"/>
                        <!--give back the space-->
                        <xsl:text> </xsl:text>
                       
                        <!--2nd word-->
                        <xsl:value-of select="substring-before( 
substring-after ($string, ' '), ' ')"/>
                        <!--give back the space-->
                        <xsl:text> </xsl:text>
                       
                        <!--3rd word-->
                        <xsl:value-of select="substring-before( 
substring-after ( substring-after ($string, ' '), ' '),' ')"/>
                        <!--give back the space-->
                        <xsl:text> </xsl:text>
                    </b>
                </div>
            </xsl:when>
            <xsl:otherwise>
                <xsl:call-template name="para.template">
                </xsl:call-template>
            </xsl:otherwise>
  </xsl:choose>
</xsl:template>
I don't know what your template name="para.template" does, but if you 
only want to split the words on the first paragraph of every chapter, 
and just copy all the others, you could do with an identity template and 
a match like David suggested:
<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" 
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
   <xsl:output method="xml" version="1.0" encoding="utf-8" indent="yes"/>
   <xsl:strip-space elements="*"/>
   <xsl:param name="split" select="3"/>
   <!-- identity template: copy all elements -->
   <xsl:template match="*">
       <xsl:copy>
           <xsl:copy-of select="@*"/>
           <xsl:apply-templates/>
       </xsl:copy>
   </xsl:template>
   <!-- override on first paragraph of each chapter -->
   <xsl:template match="chapter/section[1]/para[1]//text()[1]">
       <xsl:call-template name="splitwords"/>
   </xsl:template>
   <xsl:template name="splitwords">
       <xsl:param name="i" select="0"/>
       <xsl:param name="str1" select="''"/>
       <xsl:param name="str2" select="normalize-space(.)"/>
       <xsl:choose>
           <xsl:when test="$i = $split">
               <b><xsl:value-of select="$str1"/></b>
               <xsl:value-of select="$str2"/>
           </xsl:when>
           <xsl:otherwise>
               <xsl:choose>
                   <xsl:when test="contains($str2,' ')">
                       <xsl:call-template name="splitwords">
                           <xsl:with-param name="i" select="$i+1"/>
                           <xsl:with-param name="str1" 
select="concat($str1,substring-before($str2,' '),' ')"/>
                           <xsl:with-param name="str2" 
select="substring-after($str2,' ')"/>
                       </xsl:call-template>
                   </xsl:when>
                   <xsl:otherwise>
                       <xsl:call-template name="splitwords">
                           <xsl:with-param name="i" select="$split"/>
                           <xsl:with-param name="str1" 
select="concat($str1,$str2)"/>
                           <xsl:with-param name="str2" select="''"/>
                       </xsl:call-template>
                   </xsl:otherwise>
               </xsl:choose>
           </xsl:otherwise>
       </xsl:choose>
   </xsl:template>
</xsl:stylesheet>
HTH,
Anton