Standardised Variation Sequences with Toggles

[Andrew West]

On 16 August 2015 at 23:50, Richard Wordingham
<richard.wordingham at ntlworld.com> wrote:
>
>> @+ For details about the implementation of variation sequences in
>> Phags-pa, please refer to the Phags-pa section of the core
>> specification.
>
> a) This is likely to be ignored by someone who is just looking for the
> *specification*.  I think replacing 'implementation' by 'rendering'
> would be better.  I would be inclined to add, 'These sequences are more
> complicated than they appear at first reading'.  Otherwise, someone
> will just add them to the character to glyph conversion section of a
> font and think, "Job done".

That's not a plausible scenario. Phags-pa has complex shaping and
joining requirements, and it is impossible for someone to create a
properly functioning Phags-pa font based on the code charts alone. If
anyone did implement Phags-pa in a font based solely on the Unicode or
10646 code charts, with no joining or shaping behaviour, for use as a
fallback font or as a code chart font then naively implementing U+A856
+ U+FE00 (VS1) as a mirrored glyph is not unreasonable.  If they want
to produce a Phags-pa font for displaying running Phags-pa text then
at a minimum they will need to read the appropriate section of the
core specification.

Andrew