What do people do about warnings?

[Michael Kay]

> The really odd thing was that
> 
>   let $w := (trace($node, $message))
>   return if ($w) then () else ()
> 
> Causes a fatal error when $node is a sequence of items (in 
> this case a pair of URIs as in ($uri1, $uri2) in which both 
> were of type xs:anyURI.  

Evaluating the effective boolean value of any sequence of atomic values of
length greater than one is a dynamic error! That's nothing to do with
trace().

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