[HarfBuzz] Tai Tham NGA, SAKOT is not Kinzi

[Martin Hosken]

Dear Richard and Thep,

> In a Lanna tutorial [1], it's stated in page 12 that MAI KANG LAI is placed on
> the second consonant only. But the position is actually in the middle.
> 
>   [1] http://dl.dropbox.com/u/12266813/TaiTham/lanna-tutorial.pdf

I think this is a wrong analysis. On p23 of the same pdf the last example shows the mai tang lai over the following glyph which is an -e vowel. So clearly the mai tang lai is not associated with the second consonant. In my analysing this character I came to the conclusion that for Lanna, Khuen and Lue, mai kang lai is a final on the first consonant, even if it hangs out to the right quite a long way.

> For Lao Tham, [2] on page 14, [3] on page 15, it's clearly placed on the
> second consonant.
> 
>   [2] http://www.laomanuscripts.net/downloads/tham_pali.pdf
>   [3] http://www.esansawang.in.th/esanweb/es3_text/palitx_web.pdf

Is this Lao Tham or Isaan? Anyway, it's a new discovery to me, so thank you for finding it.

It's tricky to decide how to mark this ordering. I think we have two choices to make:

1. We don't encode the difference. We keep the mai tang lai encoded after the first consonant (which also puts it in front of the second consonant, so the encoding position is unchanged) and we say that the difference in rendering position is stylistic. Thus an OT engine would need a specific feature to trigger the reordering (given that GPOS can't attach forwards, only backwards).

2. We encode the difference. I like Thep's suggestion of using sakot for this. Thus an encoding of C1, vowels, mai kang lai, sakot, C2

The difference in position *is* stylistic. As to whether it's based purely on language or whether it's language and style, I don't know. But the difference in position carries no meaning. This would argue for approach 1. On the other hand, such a radical rendering difference can be argued as being a spelling difference, and this favours approach 2. Approach 2 is also easier for an OpenType engine. But it is harder for users who would have to use a special keyboard to do the reordering. Mind you they would have to have that for approach 1 also, so there's nothing to be gained there.

My natural inclination is to keep the data clean and go with approach 1.

What do you guys think?

Yours,
Martin