Multiple Preposed Marks

[Richard Wordingham]

On Wed, 9 Nov 2016 00:00:01 +0100
Philippe Verdy <verdy_p at wanadoo.fr> wrote:

> 2016-11-08 9:30 GMT+01:00 Richard Wordingham <
> richard.wordingham at ntlworld.com>:
> 
> > TUS Section 2.11 says, "If the combining characters can interact
> > typographically—for example, U+0304 combining macron and  U+0308
> > combining  diaeresis — then  the  order  of  graphic  display  is
> > determined  by  the  order  of  coded  characters  (see Table 2-5).
> > By  default,  the  diacritics  or other combining characters are
> > positioned from the base character’s glyph outward".
 
> The interpretation of   "If the combining characters can interact
> typographically" should be better read as "If the combining
> characters have the same non-zero combining class or any one of them
> has a zero combining class".

The combining marks in question both have canonical combining class 0.

> But now normalization is everywhere and causes the pairs using the
> condition above to be freely reordered (or decomposed and recomposed,
> meaning that the encoding order is NOT significant at all).

I believe a renderer is permitted to treat canonically equivalent
sequence differently so long as it does not believe it should treat
them differently.  However, that is irrelevant to this case.

Richard.