Re: [css-will-change] 'will-change' and custom properties

On Friday 2015-12-04 14:20 -0800, Tab Atkins Jr. wrote:
> On Tue, Nov 24, 2015 at 3:44 PM, L. David Baron <dbaron@dbaron.org> wrote:
> > https://drafts.csswg.org/css-will-change/#valdef-will-change-custom-ident
> > defines the behavior of 'will-change: <custom-ident>'.  It has a
> > number of statements that "If a[ny] non-initial value of a property
> > would cause"...
> >
> > Xidorn pointed out to me in
> > https://bugzilla.mozilla.org/show_bug.cgi?id=1227501 that
> > technically this applies to custom properties, but it probably isn't
> > meant to.  I don't think implementations should be required to trace
> > through the uses of a custom property to see if the custom property
> > could possibly cause the creation of a stacking context or the
> > generation of a containing block for fixed-positioned elements.
> > That seems like a lot of work for very little benefit... and
> > will-change is intended to make things faster, not slower!
> >
> > I think this definition should explictly exclude custom properties
> > from having these effects.
> 
> Agreed, it's not intended that that line apply to such extreme "action
> at a distance" effects.
> 
> I've specced that custom property names must have no effect, including
> the side-effect things.  That work?

That works, although I think it could be clearer, since
""side-effect" management" isn't really defined.  Perhaps replace:

  Specifying a custom property must have no effect, including the
  "side-effect" management detailed below.

with something more like:

  Specifying a custom property must have no effect, which means that
  effects that happen through custom properties do not count for the
  rules below that are conditioned on any non-initial value of a
  property causing something.

(It also might help to change the fourth such rule (for "rendering
differences") to use "If any" (like the other three rules) instead
of "If a".)

-David

-- 
𝄞   L. David Baron                         http://dbaron.org/   𝄂
𝄢   Mozilla                          https://www.mozilla.org/   𝄂
             Before I built a wall I'd ask to know
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