WPT details: 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.
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.
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
Samples: https://people.igalia.com/fwang/mathml-operator-mirroring-explainer.html