Re: A really micro schema language

On Wed, Jan 9, 2013 at 12:37 PM, John Cowan <cowan@mercury.ccil.org> wrote:

> James Clark scripsit:
>
> > Though it pains me to say it, I suspect the most appropriate MicroXPath
> is
> > CSS3 selectors.
>
> The trouble there AFAICT is that selectors allow you to refer to element
> F contained in element E (with the path "E F"), but there is no way
> to talk about an element E which contains an F.  In XPath terms, the
> only predicates are attribute-based predicates.  Also the CSS3 design
> suffers from the second-system effect: it was just enhanced without being
> redesigned, and would be awkwardly big to just adopt.  MicroXML demands
> something with more conceptual integrity, I think.
>
> --
> John Cowan  cowan@ccil.org  http://ccil.org/~cowan
> In the sciences, we are now uniquely privileged to sit side by side
> with the giants on whose shoulders we stand.
>         --Gerald Holton
>
>

Selectors level 4 has a "subject" selector (:has essentially, but even
simpler) - though it seems no one is in a rush to implement it despite it
being such a requested feature because of the performance implications.  It
is very likely that DOM's queryselectors will support a superset which are
more powerful - the problem is essentially that pages are rendered as read
so the process of applying them without making the page do crazy jumping
jacks and spasms has to be really quick - the number of comparisons/rules
that are evaluated on startup of an average page is insane and selectors
like this leave no way to know without reading the entire tree in some
cases whether a rule is true or not.


-- 
Brian Kardell :: @briankardell :: hitchjs.com