Ken Whistler recently said:
> > 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.
I'd like to suggest a particular example to clarify what you expect to happen.
If the computer is asked to render toeroen (which is the penultimate word on
page 547 of "The World's Writing Systems", Daniels and Bright.), what do you
expect the display to look like?
I think the characters are U+1832 U+1825 U+1837 U+1825 U+1828 (I'm not sure
about the n). My particular interest is the first U+1825. When there is no
preceding vowel in the word, this character takes on a different medial form
to distinguish it from the male U+1823. This is a normal behaviour of
Mongolian. The different form is listed as being available with the use of a
varient selector in the Unicode table.
Would you expect the rendering software to spot there was no preceding vowel
in the word and automatically select the correct medial glyph? Or would you
expect the software to display the default medial glyph for U+1825 which
looks like that for U+1823 and the user would have to include a varient
selector 1 to achieve the desired result?
Or to put it another way are the varient selectors rarely used (for unusual
situations) or more frequently used for any situation where the default
glyph in that position is not the desired one?
I think this depends on whether the rendering software simply treats
Mongolian as like Arabic with alternate glyphs available for selection, or
has a deeper knowledge of the appearance of Mongolian. I believe Unicode
should take an explicit position on this as it has important implications
for successful rendering of plain text on various platforms. (If the deeper
knowledge position is taken, which I think is of significant benefit to the
user, then the exact rules that are to be supported need to be stated.)
The UNU/IIST report 170 takes a third position on the issue and in section 5
seems to misunderstand Unicode's distinction between characters and glyphs
and suggests the input method selects appropriate characters including some
from the PUA for "presentation forms and ligatures". This appears to me to
be akin to a web font trick.
Tim
-- Tim Partridge. Any opinions expressed are mine only and not those of my employer
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