>     Bruce> So what I want to do is is define an output-format
>     Bruce> parameter in my main stylesheet (as above).
> 
> Perhaps you could get the effect you want by an auxiliary document.
> The fn:doc function (but NOT the document function) is in scope for
> use-when, so you could contruct an XPath expression which tested the
> value of an attribute within the auxiliary document.

Actually, the spec says that in the dynamic context for the use-when
expression, "available documents" is empty, which means that fn:doc() should
always return an error "document not found".

But it looks as if neither of the two existing implementations (mine will be
out shortly!) impose that restriction.

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