Intent to Ship: Mirroring of RTL MathML operators

56 views
Skip to first unread message

Chromestatus

unread,
Oct 31, 2025, 6:03:19 AM (6 days ago) Oct 31
to blin...@chromium.org, e...@igalia.com, fw...@igalia.com
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 desktop144
DevTrial on desktop140
Shipping on Android144
DevTrial on Android140
Shipping on WebView144
Shipping on iOS144


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

unread,
Nov 4, 2025, 8:55:13 AM (2 days ago) Nov 4
to e...@igalia.com, fw...@igalia.com, blink-dev

Hello,

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

--
You received this message because you are subscribed to the Google Groups "blink-dev" group.
To unsubscribe from this group and stop receiving emails from it, send an email to blink-dev+...@chromium.org.
To view this discussion visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/69048958.710a0220.23debc.007c.GAE%40google.com.

Chris Harrelson

unread,
Nov 5, 2025, 8:56:18 AM (23 hours ago) Nov 5
to Mike Taylor, e...@igalia.com, fw...@igalia.com, blink-dev

Yoav Weiss (@Shopify)

unread,
Nov 5, 2025, 11:33:28 AM (20 hours ago) Nov 5
to blink-dev, Chris Harrelson, e...@igalia.com, fw...@igalia.com, blink-dev, Mike Taylor
LGTM2

To unsubscribe from this group and stop receiving emails from it, send an email to blink-dev+unsubscribe@chromium.org.

--
You received this message because you are subscribed to the Google Groups "blink-dev" group.
To unsubscribe from this group and stop receiving emails from it, send an email to blink-dev+unsubscribe@chromium.org.

Philip Jägenstedt

unread,
Nov 5, 2025, 12:16:00 PM (20 hours ago) Nov 5
to Yoav Weiss (@Shopify), blink-dev, Chris Harrelson, e...@igalia.com, fw...@igalia.com, Mike Taylor
LGTM3

LGTM2

To unsubscribe from this group and stop receiving emails from it, send an email to blink-dev+...@chromium.org.

--
You received this message because you are subscribed to the Google Groups "blink-dev" group.
To unsubscribe from this group and stop receiving emails from it, send an email to blink-dev+...@chromium.org.

--
You received this message because you are subscribed to the Google Groups "blink-dev" group.
To unsubscribe from this group and stop receiving emails from it, send an email to blink-dev+...@chromium.org.
To view this discussion visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/39e0c121-29ec-46e9-ae30-f4a0f4e179c0n%40chromium.org.
Reply all
Reply to author
Forward
0 new messages