In article <D6adnVtO6Od7U0fbnZ2dnUVZ_jSdnZ2d@c...>,
Joe Kesselman  <keshlam-nospam@c...> wrote:

>By the way, if you're implementing XPath, watch out for the definition 
>of //. (I'm still trying to find someone who can explain to me why this 
>operation was explicitly defined as a top-down scan rather than as a 
>traditional postorder tree walk. Both are perfectly reasonable 
>operations, but I would expect the latter to be more commonly used and 
>hence a better meaning for the shorthand // operator. And having to 
>constantly remind folks that it *isn't* just document-ordered 
>descendant:: has been an ongoing nuisance.)

I'm not sure I understand your description, but if you mean "why is it
defined as descendant-or-self::node()/ rather than descendant::", it's
so that expressions like //p[1] mean "all paragraphs that are first
children" rather than "the first paragraph".  I believe this was
considered more common in formatting, and practical to implement as a
match pattern (predicates in match patterns can only occur after
child:: or attribute:: steps, so position() only requires examination
of siblings, rather than the whole tree).

-- Richard


-- 
"Consideration shall be given to the need for as many as 32 characters
in some alphabets" - X3.4, 1963.