[USE] Reordering of multiple pre-base vowels not specified

[NorbertLindenberg]

The standard cluster defined for the Universal Shaping Engine allows multiple pre-base vowels. However, the section “Property-based reordering” does not specify the order of such vowels after reordering – whether they remain in the same order or whether the order is inverted.

Testing with the Balinese vowels ᬾ and ᬿ showed that CoreText and HarfBuzz invert the order of the vowels, while DirectWrite keeps them in the same order.

The Unicode Standard version 13, section 2.11, page 53 states: “By default, the diacritics or other combining characters are positioned from the base character’s glyph outward.” For pre-base vowels, this would imply that the glyph order is inverted from the encoding order.

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• ID: 194a6d3c-4137-46e9-3a4b-44b990200986
• Version Independent ID: a0c8e788-5228-aa28-670e-3ba1ac3faecd
• Content: Creating and supporting OpenType fonts for the Universal Shaping Engine - Typography
• Content Source: typographydocs/script-development/use.md
• Product: typography

[xadxura]

I agree with this feedback. The principle of ordering outward from the nucleus of the syllable should apply. The Safari and HarfBuzz implementations are doing this. DWrite is not. This needs to be clarified in the spec and DWrite should be fixed.