[HarfBuzz] Thai shaping and dotted circle

[Richard Wordingham]

On Sat, 5 Oct 2013 08:48:31 +0700
James Clark <jjc at jclark.com> wrote:

> On Tue, Oct 1, 2013 at 3:22 AM, Richard Wordingham <
> richard.wordingham at ntlworld.com> wrote:

> > in Tai Lue in the Lao script combinations of tone
> >  marks do occur.

> I'm curious: are these stacked on top of each other, or are they
> side-by-side?

I don't recall seeing pictures, and I can't work out how to find a
discussion about them.  As there was some uncertainty about the
encoding order, I can only assume they were stacked vertically.  At
http://scripts.sil.org/ThaiLaoSeq the same phenomenon is recorded for
Tai Dam (or have I confused Tai Dam and Tai Lue?), and the marks are
described as being 'stacked'.  Encoding sequences are given,
with MAI EK and MAI THO preceding MAI CATAWA.

I gather that the logic is that MAI CATAWA is reinterpreted as marking
the difference between high and low consonants, though I don't know the
details.  The problem is that in these minority languages, /k/
regularly occurs with all six tones in inherited words, and single,
existing Lao tone marks only allow one to distinguish five tones.

Even in standard Lao, there is a strong tendency to write nominally
stacked marks from left to right when space is limited, even invading
the airspace of the following character.  Thai can also show this
phenomenon, though it does not seem so frequent.

Richard.