On Tue, 15 May 2018 04:19:42 -0800 James Kass via Unicode <unicode@unicode.org> wrote:
> On Mon, May 14, 2018 at 11:31 AM, Richard Wordingham via Unicode > <unicode@unicode.org> wrote: > > I've seen an implementation of the USE render > > canonically equivalent strings differently. ... > Because the USE failed or because the font provided look-ups for each > of those strings to different glyphs? Unless I haven't picked up a recent change, neither Microsoft (by evidence of MS Edge) nor Apple (by evidence of Safari in iOS 10.3.2) normalises Tai Tham text. <Tone, SAKOT> gets just one dotted circle, while Apple and Microsoft award a dotted circle to each mark in the canonically equivalent <SAKOT, tone>. Not many fonts handle two dotted circles - subscript formation has to work in the context <DOTTED CIRCLE, SAKOT, DOTTED CIRCLE, tone, base>. There's also the formal problem that <DOTTED CIRCLE, SAKOT, DOTTED CIRCLE, tone> is actually a legitimate sequence in the backing store. The defence to a charge of violating the character identity of DOTTED CIRCLE would be to say that such sequences are not supported - a renderer is not required to support all strings! Incidentally, I've fixed the Lamphun font; it will now install in Windows 10. TTX found ways to reduce its size by 10%. While it should work for most text, there are a few sequences that aren't handled properly. These are issues that pertain to the font domain, not the domain of the rendering engine. Richard.
