Chorasmian cursive joining often fails

[dscorbett]

Font

NotoSansChorasmian-Regular.otf

Where the font came from, and when

Site: https://github.com/googlefonts/noto-fonts/blob/c8daccda0216efa71254f625e4ffaba2782c2090/unhinted/otf/NotoSansChorasmian/NotoSansChorasmian-Regular.otf
Date: 2021-12-23

Font version

Version 1.000

Issue

This font never produces the final form of aleph. This is because the final form of aleph is not attested. However, L2/18-164R2 says that “an artificial cursive joining glyph must be created” because that is what the encoding model demands for consistency.

In this font, the letter after a gimel is never joined to the gimel. This is half correct: the gimel left-joins at its top instead of at the baseline, so the following letter should indeed not take its usual medial/final glyph. However, in this font, the following letter uses its initial/isolated glyph, causing an inappropriate gap after the gimel.

Similarly, aleph fails to join with the next letter if the join would be above the baseline, as in <aleph, he>.

This font does not include the initial/medial forms of taw with a leftwards joining baseline. It only includes the forms with trimmed left edges. This form only works with certain following letters for which this font provides ligatures. Some taw ligatures in the Unicode proposal are not included in this font: those with yodh, nun, and pe.

This font never cursively joins letters and numbers to each other as is required by the cursive joining model.

This font ignores ZWJ.

Character data

𐾰𐾰
U+10FB0 CHORASMIAN LETTER ALEPH
U+10FB0 CHORASMIAN LETTER ALEPH

𐾳𐾶
U+10FB3 CHORASMIAN LETTER GIMEL
U+10FB6 CHORASMIAN LETTER WAW

𐾰𐾵
U+10FB0 CHORASMIAN LETTER ALEPH
U+10FB5 CHORASMIAN LETTER HE

𐿄𐾲 𐿄𐾺 𐿄𐾾 𐿄𐿁
U+10FC4 CHORASMIAN LETTER TAW
U+10FB2 CHORASMIAN LETTER BETH
U+0020 SPACE
U+10FC4 CHORASMIAN LETTER TAW
U+10FBA CHORASMIAN LETTER YODH
U+0020 SPACE
U+10FC4 CHORASMIAN LETTER TAW
U+10FBE CHORASMIAN LETTER NUN
U+0020 SPACE
U+10FC4 CHORASMIAN LETTER TAW
U+10FC1 CHORASMIAN LETTER PE

𐾲𐿉
U+10FB2 CHORASMIAN LETTER BETH
U+10FC9 CHORASMIAN NUMBER TEN

‍𐾰‍
U+200D ZERO WIDTH JOINER
U+10FB0 CHORASMIAN LETTER ALEPH
U+200D ZERO WIDTH JOINER

Screenshot

[simoncozens]

I've done some work to move this towards a standard (Arabic-style) orthographic shaping model, but it's incomplete, so I'm leaving this issue open for now.