> Now I want to include a certain header (lika a javascript-block) in
> each of them (lets call it header.xsl).

You can do the following:

<!DOCTYPE xsl:stylesheet [
<!ENTITY header SYSTEM "header.txt">
]>

<xsl:stylesheet 
  xmlns:xsl="http://www.w3.org/XSL/Transform/1.0"
  result-ns="">


<xsl:template match="foo">
&header;
<xsl:apply-templates/>
</xsl:template>


</xsl:stylesheet>

however note that

1) If your xsl engine uses a validating parser on the XSL file, you need
   to add a SYSTEM entry to that DOCTYPE pointing at a a DTD that
   matches the stylesheet you are using.

2) The header `text' file is still parsed as XML, so you still need to
   be careful of quoting < and &.

3) This is using general XML features rather than an XSL include
   mechanism, it is probably easier to put your header into a named
   template in an xsl file and then use the XSL import mechanism to
   include this into your stylesheets, then just access the header by
   calling the named template.

David


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