[css-size-adjust] Specifying text-size-adjust: <percentage>

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[css-size-adjust] Specifying text-size-adjust: <percentage>

Philip Rogers-2
The text-size-adjust CSS keyword has a prefixed implementation in most major engines today (an exception being chromium) which lets authors control how adjustment works. The <percentage> value is currently underspecified and I'd like to spec it to match both Trident and WebKit.

Ideally, we'd remove <percentage> but the httparchive data shows percentage values are pretty common (1.2% of all files [1]). Because the implementation is not too onerous and supporting percentages with ease the transition to unprefixed properties, I'd like to spec it instead of remove it.

I'd like to define <percentage> as a set value that gets multiplied by the specified font size. Percentage values are not relative to any other adjustment and text-size-adjust: 100% is equivalent to text-size-adjust: none. Trident and WebKit appear use this logic [2] and it is compatible with existing pages and MS/MDN documentation [3,4]. For posterity, Gecko does not support <percentage> and Chromium does not yet implement text-size-adjust at all.

I have a preview of this change at:
And a preview of the updated spec at:

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Re: [css-size-adjust] Specifying text-size-adjust: <percentage>

Tab Atkins Jr.
On Mon, Jan 4, 2016 at 10:22 AM, Philip Rogers <[hidden email]> wrote:

> The text-size-adjust CSS keyword has a prefixed implementation in most major
> engines today (an exception being chromium) which lets authors control how
> adjustment works. The <percentage> value is currently underspecified and I'd
> like to spec it to match both Trident and WebKit.
>
> Ideally, we'd remove <percentage> but the httparchive data shows percentage
> values are pretty common (1.2% of all files [1]). Because the implementation
> is not too onerous and supporting percentages with ease the transition to
> unprefixed properties, I'd like to spec it instead of remove it.
>
> I'd like to define <percentage> as a set value that gets multiplied by the
> specified font size. Percentage values are not relative to any other
> adjustment and text-size-adjust: 100% is equivalent to text-size-adjust:
> none. Trident and WebKit appear use this logic [2] and it is compatible with
> existing pages and MS/MDN documentation [3,4]. For posterity, Gecko does not
> support <percentage> and Chromium does not yet implement text-size-adjust at
> all.
>
> I have a preview of this change at:
> https://github.com/progers/csswg-drafts/commit/1f80533bc0f5eb8e97fbf4ae113af5f731756140
> And a preview of the updated spec at:
> https://rawgit.com/progers/csswg-drafts/master/css-size-adjust/Overview.html#adjustment-control

I recommend instead writing:

> User agents must not do automatic size adjustment.  The computed value of font-size must be multiplied by the percentage.
>
> Note: This means that ''font-size-adjust: 100%;'' is equivalent to ''font-size-adjust: none;''.

~TJ

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Re: [css-size-adjust] Specifying text-size-adjust: <percentage>

Philip Rogers-2
Thanks Tab!

I've updated the wording (changed slightly to match the terms used in the spec):

Anyone else have thoughts on this change?

On Mon, Jan 4, 2016 at 1:13 PM, Tab Atkins Jr. <[hidden email]> wrote:
On Mon, Jan 4, 2016 at 10:22 AM, Philip Rogers <[hidden email]> wrote:
> The text-size-adjust CSS keyword has a prefixed implementation in most major
> engines today (an exception being chromium) which lets authors control how
> adjustment works. The <percentage> value is currently underspecified and I'd
> like to spec it to match both Trident and WebKit.
>
> Ideally, we'd remove <percentage> but the httparchive data shows percentage
> values are pretty common (1.2% of all files [1]). Because the implementation
> is not too onerous and supporting percentages with ease the transition to
> unprefixed properties, I'd like to spec it instead of remove it.
>
> I'd like to define <percentage> as a set value that gets multiplied by the
> specified font size. Percentage values are not relative to any other
> adjustment and text-size-adjust: 100% is equivalent to text-size-adjust:
> none. Trident and WebKit appear use this logic [2] and it is compatible with
> existing pages and MS/MDN documentation [3,4]. For posterity, Gecko does not
> support <percentage> and Chromium does not yet implement text-size-adjust at
> all.
>
> I have a preview of this change at:
> https://github.com/progers/csswg-drafts/commit/1f80533bc0f5eb8e97fbf4ae113af5f731756140
> And a preview of the updated spec at:
> https://rawgit.com/progers/csswg-drafts/master/css-size-adjust/Overview.html#adjustment-control

I recommend instead writing:

> User agents must not do automatic size adjustment.  The computed value of font-size must be multiplied by the percentage.
>
> Note: This means that ''font-size-adjust: 100%;'' is equivalent to ''font-size-adjust: none;''.

~TJ

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Re: [css-size-adjust] Specifying text-size-adjust: <percentage>

L. David Baron
On Friday 2016-01-08 16:45 -0800, Philip Rogers wrote:

> Thanks Tab!
>
> I've updated the wording (changed slightly to match the terms used in the
> spec):
> change:
> https://github.com/progers/csswg-drafts/commit/bd192715923dbe0af1207fce195dbb11a3a4fab1
> preview:
> https://rawgit.com/progers/csswg-drafts/master/css-size-adjust/Overview.html#adjustment-control
>
> Anyone else have thoughts on this change?
Sorry for the delay here.

I guess this seems reasonable if that's what the compatible behavior
is, except it needs to be conditional on "when displaying on a small
device" (which itself may need to be defined better).  That's
because this definition (even more than the others) is dependent on
when text size adjustment "happens" vs.  "doesn't happen".

(Also, presumably Tab's wording needs
s/font-size-adjust/text-size-adjust/.)

-David

> On Mon, Jan 4, 2016 at 1:13 PM, Tab Atkins Jr. <[hidden email]> wrote:
>
> > On Mon, Jan 4, 2016 at 10:22 AM, Philip Rogers <[hidden email]> wrote:
> > > The text-size-adjust CSS keyword has a prefixed implementation in most
> > major
> > > engines today (an exception being chromium) which lets authors control
> > how
> > > adjustment works. The <percentage> value is currently underspecified and
> > I'd
> > > like to spec it to match both Trident and WebKit.
> > >
> > > Ideally, we'd remove <percentage> but the httparchive data shows
> > percentage
> > > values are pretty common (1.2% of all files [1]). Because the
> > implementation
> > > is not too onerous and supporting percentages with ease the transition to
> > > unprefixed properties, I'd like to spec it instead of remove it.
> > >
> > > I'd like to define <percentage> as a set value that gets multiplied by
> > the
> > > specified font size. Percentage values are not relative to any other
> > > adjustment and text-size-adjust: 100% is equivalent to text-size-adjust:
> > > none. Trident and WebKit appear use this logic [2] and it is compatible
> > with
> > > existing pages and MS/MDN documentation [3,4]. For posterity, Gecko does
> > not
> > > support <percentage> and Chromium does not yet implement
> > text-size-adjust at
> > > all.
> > >
> > > I have a preview of this change at:
> > >
> > https://github.com/progers/csswg-drafts/commit/1f80533bc0f5eb8e97fbf4ae113af5f731756140
> > > And a preview of the updated spec at:
> > >
> > https://rawgit.com/progers/csswg-drafts/master/css-size-adjust/Overview.html#adjustment-control
> >
> > I recommend instead writing:
> >
> > > User agents must not do automatic size adjustment.  The computed value
> > of font-size must be multiplied by the percentage.
> > >
> > > Note: This means that ''font-size-adjust: 100%;'' is equivalent to
> > ''font-size-adjust: none;''.
> >
> > ~TJ
> >
--
𝄞   L. David Baron                         http://dbaron.org/   𝄂
𝄢   Mozilla                          https://www.mozilla.org/   𝄂
             Before I built a wall I'd ask to know
             What I was walling in or walling out,
             And to whom I was like to give offense.
               - Robert Frost, Mending Wall (1914)

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