> Well this one is interesting since in XPath 2 F&O spec it is said that
> 
> [[
> Thus, the semantics " $a idiv $b " are equivalent to " ($a 
> div $b) cast as xs:integer " except for error situations.
> ]]
> 
> A bug in the spec or in Saxon ?

I have raised a bug report against the spec at

http://www.w3.org/Bugs/Public/show_bug.cgi?id=6212

The bug report suggests changing this sentence to a non-normative note:

Note: this means that the expression "$a idiv $b" gives the same result as
"($a
div $b) cast as xs:integer" except possibly in situations involving errors,
overflow/underflow, or loss of precision. 

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