RE: Make its:param optional?

On Fri, 2012-10-12 at 05:31 -0600, Yves Savourel wrote:
> Hi Felix, Jirka, Shaun, all,
> 
> > OK, so we keep its:param I guess. 
> > Would it be OK to add the following note to the its:param section:
> >
> > its:param adds flexibility in real-life situations. However in general 
> > it is recommended not to use its:param. It is disallowed in CSS, 
> > see section 5.3.5, since the current version of CSS does not allow 
> > variable bindings.
> 
> Hum, I have nothing about a note touching on the difficulty of implementation. But the CSS part, I think, is a different story. It sounds like the fact its:param is not part of ITS-with-CSS is a valid reason to not use it with XPath either. That's a bit strong for a best practice.
> 
> -- a) Likely, its:param is going to be used only in the cases where
> there is no other way to write the rule. So it'll be for use cases
> where you can't use CSS anyway. So re-suing those rules doesn't really
> applies.

I think its:param is useful for very specific stuff. And hopefully
when you're dealing with specifics, you know your ITS processing
tool and what it can do.

But if you're creating ITS files for interchange (for example, if
you create an XML vocabulary and you provide reference ITS rules
for it), then you should avoid its:param.

> -- b) You can make a rule that uses its:param not use it by just
> replacing the variable by a given value, then you convert that to CSS.
> It's not much more work than actually converting the XPath selector to
> a CSS selector. Sure it's not a 1-to-1 port of the rules, but the
> point is that first: its:param is not a show-stopper, and second: if
> someone wants to convert XPath-based rules to CSS-based rules, the
> hard part is to convert XPath to CSS, not its:param.
> 
> -- c) Why its:param cannot be used in CSS in the first place? CSS may
> not have a binding mechanism but what's preventing CSS implementers to
> use the mechanism Jirka described in
> http://lists.w3.org/Archives/Public/public-multilingualweb-lt/2012Oct/0148.html? In most programming languages it's simple to substitute the variables by their values before applying the selectors. If I were an implementor of a CSS-based ITS engine I would be puzzled by the section 5.3.5.

There's just no agreed-upon syntax for variables in CSS selectors.
You could pretend that $ is an XPath-like variable sigil and do a
substitution pre-pass, but it's really not a CSS selector anymore.

I'm not aware of any efforts to introduce variables for selectors.
Jirka mentioned CSS variables might exist in the future, but the
only effort I know of is about adding variables in properties,
not selectors:

http://dev.w3.org/csswg/css-variables/

> -- d) Do we have anyone implementing ITS with CSS selectors? If we
> don't at this stage, I wonder if any CSS-based argument is applicable.

I implemented it in Jits, except without CSS selector namespace
support, because querySelectorAll doesn't do namespaces. But I'm
not actually using ITS files with CSS selectors for anything.

--
Shaun

Received on Friday, 12 October 2012 19:54:01 UTC