[Mod_transform] Apache warning: [mod_transform: Warning, no content type was set! Fix your XSLT!] - what does this mean?

[perry.tew at cibavision.com]

Hey,
  Nice module.  I just installed it.  Thanks for writing it.   I received 
the following warning in my apache log when testing out the module.  The 
transformation was successful.

mod_transform: Warning, no content type was set! Fix your XSLT!

Can you elaborate on how I can fix my xslt?  I'm not sure what I should 
put into my xslt file.  I added a meta tag specifying a content tag of 
text/html, but that didn't work and was stripped out and replaced by the 
transformation.

I used the cdcatalog example from www.w3schools.com (xsl tutorial) as my 
test.
http://www.w3schools.com/xsl/xsl_transformation.asp


Here is my apache configuration, in case the problem is there.
<VirtualHost _default_:5035>

AddOutputFilter XSLT xml

<Directory "/web/devel/tewpe1/intranet/apache/htdocs/xmltest">
        TransformOptions +ApacheFS
        TransformSet /xmltest/cdcatalog.xsl
</Directory>

...


Also, the url for my test is 
http://server:5035/xmltest/cdcatalog.xml
so, Firefox is treating like an xml document (the content-type is also 
text/xml).
Do you have any strategy for getting Firefox to process it as an html 
document?  I noticed that the outoforder.cc web site used directories for 
all urls, thus avoiding the problem of file extensions.  I thought about 
using mod_rewrite.  Not all files on the server are to be transformed, so 
I hesitate to change the mime type for the .xml extension.

At any rate, thanks for your time and effort.
Perry Tew