John Hudson wrote:
> >Mongolian variants *are* very confusing, and I'm not sure what the
> >best way to describe them is. Part of the problem is that there is
> >still some tension in the UTC regarding just how to define the affect
> >of the variation selectors.
> >
> >Position A: A variation selector selects a particular, defined glyph.
> >
> >That position would, for Mongolian, tend to support your second
> >interpretation. However, ...
> >
> >Position B: A variation selector selects a variant form of a character,
> >which has a distinct rendering from that specified for the character
> >without a variant specification.
>
> The inclusion of variant selectors in Unicode uncomfortably blurs the line
> between character processing and glyph processing.
True enough. But they are an attempt to keep a finger in the dike
of outright glyph encoding. If you think of the problem with Han
variants, you can see that allowing those dike leaks to crumble the
dike could result in a veritable inundation of the character encoding
with essentially useless alternate forms that would only serve to
further blur the line. Or to extend the metaphor, the ground beneath
our feet would be so softened, we'd always be trudging around hipdeep
in the mud for CJK.
> The only excuse I can
> think of for including glyph substitution triggers in plain text is if
> there are normative stylistic substitutions to be identified by an author
> as a regular aspect of the writing of a given script, i.e. Ken's Position
> A. If you are not going to specify what the variant is, what point is there
> to including the glyph subsitution trigger in plain text, since you have no
> idea what the outcome is going to be in any given font?
Actually, I think Position B is a coherent one for Mongolian. The
outcome *is* specified -- it is just specified for particular positional
contexts, rather than for a single glyph per se.
X -> {G1, G2, G3, G4}, where Gn is determined by positional (or other) context.
X-/ -> {G1, G2', G3', G4}, where Gn is determined by positional (or other) context.
is still determinate, and not contingent on fonts. (Although, of course,
if you use fonts that don't have the glyphs G1, G2, G2', G3, G3', G4, or
software that can't do the mapping correctly, you are hosed.)
It is just more complicated, but fully as determinate as:
X -> G
X-/ -> G'
> The value of the
> variant selector to the user is in knowing what the result is going to be,
> and this means that the variant form *must* be specified.
It is. See above.
> How else can the
> variant selector be used to *select* a particular form? Selection implies a
> deliberate choice, not a willingness to accept any substitution a font
> might provide.
I agree. Although variation selectors also imply willingness to accept
fallback to default glyphs as legible alternatives, if not the
desired alternatives.
--Ken
>
> John Hudson
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