Intent to Ship: Mirroring of RTL MathML operators

[Chromestatus]

Contact emails

e...@igalia.com, fw...@igalia.com

Specification

https://w3c.github.io/mathml-core/#layout-of-operators

Summary

Support for character-level and glyph-level mirroring when rendering MathML operators in right-to-left mode. When using RTL mode some operators can be mirrored by changing them to another code point (e.g. a right parentheses becomes a left parentheses). This is character-level mirroring, with equivalences defined by Unicode's `Bidi_Mirrored` property. There are operators that have no appropriate mirroring character. Glyph-level mirroring applies in this case, with the `rtlm` font feature, where another glyph can replace it in a mirrored context. Some existing implementations mirror the original glyph directly, but this may change the meaning for asymmetrical characters, such as the clockwise contour integral.

Blink component

Blink>MathML

Web Feature ID

mathml

Motivation

Arabic mathematical notations require rendering math operator in right-to-left mode, where operators need to be correctly mirrored. Sometimes, a simple horizontal flip is not enough. In the case of asymmetrical glyphs like a clockwise contour integral doing so would change the meaning of the symbol. That's why both character-level mirroring and glyph-level mirroring is needed to produce a correct mathematical expression in RTL mode. The following explainer shows the different cases to consider when mirroring stretchy characters, as well as the proposed MathML Core spec amendments to support this use case: https://people.igalia.com/fwang/mathml-operator-mirroring-explainer.html

Initial public proposal

No information provided

TAG review

No information provided

TAG review status

Not applicable

Risks

Interoperability and Compatibility

No information provided

Gecko: Shipped/Shipping (https://bugzilla.mozilla.org/show_bug.cgi?id=945183) Shipped under the `mathml.rtl_operator_mirroring.enabled` flag. Will be enabled by default once Firefox 146 releases.

WebKit: In development Already has character-level mirroring. rtlm support is being worked on for the harfbuzz ports.

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?

No information provided

Debuggability

No information provided

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

Yes

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

Yes
New tests: - Character-level mirroring: checks that when switching text direction the codepoints of the characters change to the corresponding BidiMirrored equivalent (e.g. right to left parentheses) - Glyph-level mirroring: checks that the rtlm font feature is supported and that a specific glyph is used for certain characters when switching text direction.

Flag name on about://flags

No information provided

Finch feature name

MathMLOperatorRTLMirroring

Rollout plan

Will ship enabled for all users

Requires code in //chrome?

False

Tracking bug

https://issues.chromium.org/issues/40120782

Availability expectation

Feature already available on Firefox and partially available on WebKit, with plans to make it fully available within the next months.

Adoption expectation

Feature is used for the case of rendering right to left math.

Adoption plan

It will ship enabled by default so users can start benefiting from it.

Non-OSS dependencies

Does the feature depend on any code or APIs outside the Chromium open source repository and its open-source dependencies to function?

No.

Estimated milestones

Shipping on desktop	144
DevTrial on desktop	140
Shipping on Android	144
DevTrial on Android	140
Shipping on WebView	144
Shipping on iOS	144

Anticipated spec changes

Open questions about a feature may be a source of future web compat or interop issues. Please list open issues (e.g. links to known github issues in the project for the feature specification) whose resolution may introduce web compat/interop risk (e.g., changing to naming or structure of the API in a non-backward-compatible way).

No.

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/6317308531965952?gate=4798753084801024

Links to previous Intent discussions

Intent to Prototype: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/686d2758.170a0220.a35ba.00d7.GAE%40google.com
Ready for Trial: https://groups.google.com/a/chromium.org/g/blink-dev/c/IpmWeJSPR0g

This intent message was generated by Chrome Platform Status.

[Mike Taylor]

Hello,

Could you please request reviews for the Privacy, Security, Enterprise, Debuggability, and Testing bits in your chromestatus entry?

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[Chris Harrelson]

LGTM1

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[Yoav Weiss (@Shopify)]

LGTM2

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[Philip Jägenstedt]

LGTM3

LGTM2

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