() eq () vs () = ()

I've recently found out (over on the saxon list) that:

() eq ()

returns the empty sequence, but

() = ()

returns false.

What is the benefit of returning the empty sequence over false... when
would I want that?   It seems like an unecessary gotcha to me...
similar to xs:boolean('0') vs fn:boolean('0')

Also, this is from the xpath 2.0 spec:

"Consider the expression //part[color eq "Red"]. An implementation
might choose to rewrite this expression as //part[color = "Red"][color
eq "Red"]. The implementation might then process the expression as
follows: First process the "=" predicate by probing an index on parts
by color to quickly find all the parts that have a Red color; then
process the "eq" predicate by checking each of these parts to make
sure it has only a single color"

...which makes me wonder bother with using 'eq' at all.  I wouldn't
use it to ensure there is only one of something, that would be done
elsewhere... I always thought it allowed the comparison to be
optimised behind the scenes, but that suggests otherwise.


thanks
-- 
Andrew Welch
http://andrewjwelch.com