Re: [csswg-drafts] Browser zoom unit for accessibility [css-values-and-units] (#6869)

Since the zoom problem, not to mention at the x-height problem, is a big part of the work we've been doing, I'm putting this post here to update this thread with recent information.


The fact that browsers for the most part only zoom by a single percentage is part of the problem. The other part, is that different browsers handle their zoom of the page, or independently, zooming the text, in different ways and there's really not a standardization there.

And as some point out, and which we've been talking working on APCA / WCAG 3.0, zooming all text by a single percentage **does not serve the needs of users**. There is a range of "critical font size" and in an ideal world all text would remain within that range for that user.

But additionally, the current **200%** in WCAG 2 is really **not enough**. The difference between 20/20 and 20/40 is 200%¹ (!!) Low vision needs much more. For desktop work, 500% for body text is reasonable and useful, accommodating somebody at 20/100.²

Low vision is considered somewhere around 20/70 ~ 20/80 and worse. Technically, 20/80 could need 400% (all things being equal, of course there are a number of wiggle factors here).

Unfortunately, 400% doesn't work on mobile devices. An iPad in portrait mode or an iPhone in landscape mode is limited at about 350% (20/70). And for a phone in portrait mode, 200% is really the limit for 16px body text—and this is only considering body text. When talking about large headlines, they can't be anywhere near 200% for mobile devices. Again all things being equal depending on Display, scale, distance from the face, etc.

In this post in [***discussion 39 on use-cases***](https://github.com/Myndex/SAPC-APCA/discussions/39#discussioncomment-4500540) at the readability forum, about halfway down is the section on spatial frequency (size) and zooming, and a link to some [examples](https://www.myndex.com/WEB/TextZoomExample). 

These show that **if we really want to accommodate low vision**, we cannot be zooming all text the same percentage, period. At the moment this can't be a guideline because the technology isn't there, except with a polyfill, and we can't require a polyfill guideline. 

### What we need is browsers aligning uncommon standards for how to handle:

**_At a minimum_**
1) [**asymmetrical text zoom**]([examples](https://www.myndex.com/WEB/TextZoomExample)) with content text reflow, as described in the examples were text larger than the body text does not get zoomed as much.
2) **_full page zoom_** (text & elements on page maintain relative relationships)

**_Enhanced_**
1) **_Element text only zoom_** (a.k.a. paragraph zoom) zooms only the text of the selected text container, such as a column, leaving all other text as is, including headers.
2) **_Element adjust zoom_** style sheet that adjusts specific elements (CSS is not really here for this yet).
3) **Force reader mode for selection** 

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***NOTES:***
**¹ Regarding 20/40 & 200%**. With a standard font such as Arial or Helvetica, at 16px 400 body text, at 100% and on a standard monitor at the standard distance away, where 1px = 1.278 arc minutes of visual angle, and the luminance contrast is adequate (Lc 75+), then we're at the critical size for best **fluent** readability for 20/20, for 20/40 we need to zoom to 200%, for 20/70 we need to zoom to 350% for that body text.
***Critical size*** means that increasing the size further **_does not_** result in an improvement in fluent reading speed or comprehension. *(Lovie-Kitchin et alia)*

**² Regarding 20/100 vision**. Per the current rules with the Social Security administration in the United States: uncorrected vision in both eyes, worse than 20/100, where **no letters** on the 20/100 line are recognizable, constitutes legally blind.
The common statement of "20/200 is legally blind" stems from older eye charts that jumped straight from 20/100 to 20/200, but nothing in between. Modern LogMAR charts have intermediary lines, typically 20/125 & 20/160. For SSA disability, if somebody can see letters on 20/125, but none on 20/100, they are considered legally blind. *(US SSA)*

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Received on Tuesday, 27 December 2022 05:31:55 UTC