Including predefined HTML code into chunked HTML

Dear all,

I want to include some <!--#include virtual="/Inc/xyz.inc" --> lines 
into chunked HTML files.

For that purpose I have copied the complete <xsl:template 
name="chunk-element-content"> template from xhtml/chunk-common.xsl to my 
customization layer and edited it as follows:

After <xsl:call-template name="user.header.content"/> I added one line: 
<!--#include virtual="/Inc/header.inc" -->
Before </body> I added <!--#include virtual="/Inc/footer.inc" -->

The problem is that both include lines are not included in the resulting 
HTML chunk files.

What's my mistake?

Cheers
B.