L2/17-169

Title: Proposed Indic Syllabic Category changes for Tai Tham for Unicode 10
Author: Roozbeh Pournader (Google)
Date: May 12, 2017

I volunteered to propose changes based on L2/17-120 for Unicode 10. I have
briefly consulted the following documents as extra references: L2/04-351,
L2/05-095R, L2/06-258R, L2/07-007R, L2/07-319, L2/08-037R2, and L2/08-073, as
well as the IUC presentation by Patrick Chew, whose slides are available at
https://github.com/googlei18n/noto-fonts/files/338012/IUC39.-.Tai.Tham.pdf.

Following are my suggestions for changes in Unicode 10:

1. Change U+1A57 and U+1A5B..U+1A5E from Consonant_Final to Consonant_Subjoined.
2. Change U+1A5A from Consonant_Final to Consonant_Suffixed (new class).
3. Change U+1A61 from Vowel_Dependent to Visarga.
4. Change U+1A74 from Vowel_Dependent to Bindu.
5. Change U+1A7A from Syllable_Modifier to Pure_Killer.

My exact proposed change to IndicSyllabicCategory.txt can be seen at:
https://github.com/roozbehp/unicode-data/commit/2ba063987f0

Please note that there are clearly more changes needed for Tai Tham,
especially for the very complex case of U+1A58 TAI THAM SIGN MAI KANG LAI. But
due to limitations of time and understanding from my side, I would appreciate
postponing those to a later version of Unicode, so that we could consider them
properly.