> Googling around though, shows "top-level element" refers to 
> both  the single root element of an xml document (in error 
> messages), and the top-level child elements in xslt.... One 
> must be wrong.

No, the word "set" has about 43 meanings, and none of them is wrong. You
just have to be clear about your context. Unfortunately, google isn't.

I did try to get rid of the term in XSLT 2.0. It's still used (and defined),
but most of the time has been replaced by "declaration". Top-level element
is a slighly broader category that embraces declarations and user-defined
data elements. XML schema uses the term in much the same way, with "global"
as a near synonym.

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