Fallback for Sinhala Consonant Clusters

[Richard Wordingham via Unicode]

On Tue, 16 Oct 2018 11:59:54 +1100
Harshula via Unicode <unicode at unicode.org> wrote:

> Hi Richard,
> 
> On 16/10/18 6:57 am, Richard Wordingham via Unicode wrote:
> > On Tue, 16 Oct 2018 02:47:36 +1100
> > Harshula via Unicode <unicode at unicode.org> wrote:
> >   
> >> Note, touching letters are formed by <ZWJ><AL-LAKUNA>, so they
> >> should not be displayed as a fallback for <AL-LAKUNA><ZWJ>
> >> conjuncts.  
> > 
> > I don't follow that.  While the conjuncts with r-, -r and -y are
> > very different to pairs of touching letters, the conjuncts for tth,
> > nd, ndr, ndh, kv and tv would be very similar to the hypothetical
> > corresponding touching letters and quite different to the fallbacks
> > with visible al-lakuna.  
> 
> If you haven't already, it's best you read SLS 1134:2011:
> http://www.language.lk/en/download/standards/
> 
> or the older SLS 1134:2004:
> http://unicode.org/wg2/docs/n2737.pdf

The latter actually says, in Section 5.8, that <AL-LAKUNA, ZWJ> may be
used for either!  I suspect that that is a printing error.

The Sri Lankan standard simply assumes that the rendering system can
accommodate what is requested in the backing store.  It says nothing
about fallbacks.  So, if the user specifies the the syllable ddho
written with a conjunct and encoded as ද්‍ධො but the conjunct is
missing from the fonts' repertoires, why is it right to display it with
al-lakuna as though it were ද්ධො but wrong to display it with the
touching letters encoded as ද‍්ධො?   There are three different
correct ways of writing 'ddho', but many systems only support one of
them (and some weirdly use a fourth method). 

Richard.