This feature adds logic to ignore the letter-spacing setting for cursive scripts as specified by the web author, in line with the spec, to ensure that letter spacing does not disrupt word structure and aims to produce better user experience for users relying on cursive scripts. The spec suggests that the UA may apply letter spacing to cursive scripts by translating the total extra space into cursive elongation or compression. Otherwise, if the UA cannot expand text from a cursive script without breaking its cursive connections, it must not apply spacing between any pair of that script’s typographic letter units at all. Ignoring letter spacing altogether for cursive scripts is simpler and helps avoid performance issues as handling spacing for such scripts requires complex calculations to maintain cursive connections and account for script-specific factors like elongation glyphs, typefaces, and calligraphy preferences. With this feature, Chromium ensures that cursive scripts will be readable and properly spaced, even if the fonts don’t have advanced typographic features. The scripts that we are proposing to apply this to in Chromium are Arabic, Hanifi Rohingya, Mandaic, Mongolian, N’Ko, Phags Pa, and Syriac as these scripts are considered cursive as per spec.
Cursive scripts do not admit gaps between their letters for either justification or letter-spacing. The following Unicode scripts are included: Arabic, Hanifi Rohingya, Mandaic, Mongolian, N’Ko, Phags Pa, Syriac. If the UA can apply letter spacing to cursive scripts without breaking connections, it should elongate or compress the script accordingly. If not, it must treat each word as a single unit, resulting in zero effective spacing between letters. Implementation of Kashida justification for Arabic scripts is an alternative. However, this logic should apply to all cursive scripts, not just Arabic, hence adding this logic to ignore letter spacing even if web author wants to per spec.