Intent to ship: MathML Core math-shift: compact

[Eri Pazos Pérez]

As of today (2025-10-14), I intend to turn support for math-shift: compact on by default. It has been developed behind the mathml.math_shift.enabled preference.

Summary: Superscripts with math-shift: compact will be placed slightly lower (using the superscriptShiftUpCramped parameter from the OpenType MATH table instead of superscriptShiftUp). This property is applied to scripts in small spaces, such as radicals or fraction denominators. In TeX this is called cramped mode.

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1923569

Bug to turn on by default: https://bugzilla.mozilla.org/show_bug.cgi?id=1994171

Standard: https://w3c.github.io/mathml-core/#the-math-shift

Standards Body: W3C.

Platform coverage: All platforms.

Preference: mathml.math_shift.enabled

Other browsers:

• Blink: shipped, no flags.
• WebKit: shipped in version 227, no flags.

web-platform-tests:

• New tests to check the parsing of the property:
  • /mathml/relations/css-styling/parsing/math-shift-valid.html
  • /mathml/relations/css-styling/parsing/math-shift-invalid.html
  • /mathml/relations/css-styling/parsing/math-shift-computed.html
• Existing tests that are now passing:
  • /mathml/presentation-markup/scripts/cramped-001.html