> . Now, for each occurrence of a search query value within an element
<regel>
> (line) I want to see the contents of the parent element 
> <titel> (title).

I think that's exactly what your query does; but it doesn't seem to be what
you really want.
> 
> This, I succeed in, using this XSL:
> 
> ------------------------------------------------------------
> <xsl:for-each select="strofen/regel">
>  <xsl:variable name="line" select="."/>
>  <xsl:variable name="linelow"
> select="translate($line,'ABCDEFGHIJKLMNOPQRSTUVWXYZ','abcdefgh
> ijklmnopqrstuvwxyz')"/>
>   <xsl:if test="contains($linelow,$querylow)">
>    <xsl:copy-of select="../../titel" />
>    <br />
>   </xsl:if>
> </xsl:for-each>
> ------------------------------------------------------------
> 
> . However, this returns 1 title for each line containing the 
> query. 

It looks as if your real requirement is

<xsl:if test="strofen/regel/line[contains(lower-case(.), $querylow]">
  <xsl:value-of select="titel"/>
</xsl:if>

(where you can replace lower-case() by your translate call if you are using
XSLT 1.0)

Michael Kay
http://www.saxonica.com/