Selecting between multiple stylesheets on same xml fil

Hi... first I want to say thanx to those who solved my
xsl variable problem. Now I'm asking if there's a
similar way to declare and pass an external value to a
variable in the XML document itself.
I'm using an apache/cocoon setup, with an xml newsfeed
of about 5/6 categories of stories. With perhaps with
php script, I want to detect the user's platform, eg
normal desktop/laptop, PocketPC, Palm, etc using
HTTP_USER_AGENT, also category(s) of user's news
preferences, particular story etc, then select the
appropriate xsl stylesheet to serve up content
particular to their needs.
At the moment, i'm using several copies of the same
xml file referencing different stylesheets, and
obviously this is ridiculous! What I want to do is
something like this:

<?xml version="1.0" encoding="iso-8859-1"?>
<?xml-stylesheet href="$xyz.xsl" type="text/xsl"?>
<?cocoon-process type="xslt"?>

where $xyz is a variable which can be declared in the
xml file some way similar to the way I'm using
<xsl:param> to construct variables in the xsl that can
pick up values passed by a php script or appended to a
url e.g http://myserver.com/news.xml?xyz=stylesheet1

Thanks!

P.S. Am I approaching this wrong? Should there be just
one stylesheet reference in the xml, and then in the
stylesheet itself use variables to select between
diffent @import locations and have all the specific
templates in small external xsl files?


____________________________________________________________
Do You Yahoo!?
Get your free @yahoo.co.uk address at http://mail.yahoo.co.uk
or your free @yahoo.ie address at http://mail.yahoo.ie

 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list