- From: Tab Atkins Jr. <jackalmage@gmail.com>
- Date: Mon, 30 Sep 2013 10:59:10 -0700
- To: Cameron McCormack <cam@mcc.id.au>
- Cc: www-style list <www-style@w3.org>
On Sun, Sep 29, 2013 at 11:55 PM, Cameron McCormack <cam@mcc.id.au> wrote:
> toggle() presents some issues similar to variables regarding what specified
> values should be returned from CSSStyleDeclaration objects and how they
> should be serialised.
>
> Consider for example:
>
> <style>
> p { margin: toggle(1px 2px, 3px 4px); }
> </style>
> <script>
> alert(theRule.style.getPropertyValue("margin"));
> alert(theRule.style.getPropertyValue("margin-top"));
> </script>
>
> What should be alerted?
>
> Since we know that toggle() values are invalid (at parsing time) if any of
> their component values are invalid, then we can actually split this up into
> toggle() values for the subproperties. So we can treat the effect of the
> shorthand as being equivalent to:
>
> margin-top: toggle(1px, 3px);
> margin-right: toggle(2px, 4px);
> margin-bottom: toggle(1px, 3px);
> margin-left: toggle(2px, 4px);
>
> I don't think the spec says to do this, though. The alternative is to have
> something like Variables' "pending variable-substitution value", but it
> would be good to avoid this if possible.
>
> Based on that, I would have said that the first alert should be "toggle(1px,
> 3px) toggle(2px, 4px)", reconstructing it from the longhands, but having
> multiple toggles() isn't valid. It's not straightforward to reconstruct
> "toggle(1px 2px, 3px 4px)" from the longhands.
>
> Also it would be tricky in cases like this:
>
> p { margin-top: toggle(1px, 2px);
> margin-right: toggle(3px, 4px, 5px);
> margin-bottom: 0;
> margin-left: 0; }
>
> If getting the value of "margin", should we have to return something like:
>
> toggle(1px 3px 0 0, 2px 4px 0 0, 2px 5px 0 0)
>
> the repeated "2px" value padding out the list of margin-top values?
>
>
> And what about this:
>
> p { margin: toggle(1px 2px, 3px 4px, 1px 5px); }
>
> Should this decompose into:
>
> margin-top: toggle(1px, 3px, 1px);
> margin-right: toggle(2px, 4px, 5px);
> ...
>
> where the margin-top toggling will really only switch between two values,
> not three?
Ugh, we didn't consider longhands when putting in the prohibition
against multiple toggles in a single declaration. :/ I would prefer
we just relax that requirement and damn the consequences, though that
does mean that you have to do combinatorial amounts of syntax checking
to ensure that it's valid when specified by the author. Perhaps this
is okay?
~TJ
Received on Monday, 30 September 2013 17:59:56 UTC