Web-Facing Change PSA: text-size-adjust improvements

[Philip Rogers]

Contact emails

p...@chromium.org

Specification

https://drafts.csswg.org/css-size-adjust/#propdef-text-size-adjust

Summary

text-size-adjust adjusts font sizes on mobile devices. Values other than auto disable automatic text size adjustments. Percentage values increase the computed size of text. This makes text-size-adjust more consistent, so it works like a direct multiplier of the font size (and line height). The major changes are: * text-size-adjust works with or without a meta viewport. * non-auto values disable ALL automatic text size adjustments. * percentages apply directly, without any heuristics. * layout bugs are fixed.

Blink component

Blink>CSS

TAG review

None

TAG review status

Not applicable

Risks

Interoperability and Compatibility

The compatibility risk is low and this is likely to just appear as a bugfix to developers and users. This area is a source of confusion for developers today. The automatic text scaling applied by the browser already varies significantly with OS font scale settings and device size, so pages are unlikely to depend on the exact current behavior.

Gecko: Shipped/Shipping

WebKit: Shipped/Shipping

Web developers: No signals

Other signals:

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?

None

Goals for experimentation

Ongoing technical constraints

None

Debuggability

Text-size-adjust can be debugged via mobile emulation in devtools.

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?

No

This has historically only been supported on mobile platforms.

Is this feature fully tested by web-platform-tests?

No

There are some basic Web Platform Tests but this feature only works on mobile devices so it cannot be fully tested without "mobile" support (see: https://github.com/web-platform-tests/wpt/issues/12725 for similar issues).

Flag name on chrome://flags

Finch feature name

NewTextSizeAdjust

Requires code in //chrome?

False

Tracking bug

https://crbug.com/340389272

Estimated milestones

No milestones specified

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/5111875942744064

This intent message was generated by Chrome Platform Status.

[Philip Rogers]

Explainer doc with more information for web developers: https://docs.google.com/document/d/1l3LFl_kDDoScUlXTcBXsnj2RbeU9zXo1DqNfctY84p0/preview