From: Jungshik Shin (jshin@mailaps.org)
Date: Mon May 12 2003 - 04:22:58 EDT
On Sun, 11 May 2003, Michael (michka) Kaplan wrote:
> From: "Jungshik Shin" <jshin@mailaps.org>
>
> > Recently I found some fonts have visible glyphs for invisible characters
> > (that I _guess_ are supposed to have no visual effect) such as U+2062
> > (the glyph for U+2062 is dotted 'x' inside a dotted box). With these
> > kind of fonts present, a bit naive(??) approach of searching for glyphs
> > in all the fonts on the system would turn the 'invisible' to the visible.
> > For instance, the following MathML snippet was rendered with
> > a visible glyph (⁢ == U+2062) by Mozilla.
> >
> > <mi>a</mi><mo>⁢</mo><mi>c</mi>
>
> Yes, you mentioned this in your mails from a few days ago....
You wrote as if I had sent two emails with more or less the same
content a few days apart from each other. I didn't. Did you get two?
> > My questions are:
> >
> > (1) Is a font to blame for having visible glyphs for U+2062 and
> > similar characters. I think U+2062 and similar characters are different
> > from ZWJ/ZWNJ and other 'control' characters that do have visual effect
> > in such context as Indic scripts, Arabic script and expressing authorial
> > intent about ligature in Latin and other scripts)
>
> You did not mention specifically what font is doing this, which makes it
> hard to claim that a font should be "blamed" for anything. What is/are the
> font(s) and where did you get it/them?
At that time, I hadn't checked it out yet. Now that I've checked it,
it turned out that it's Code2000. It appears that James may have been a
bit too aggressie to put visible glyphs for U+2062( : INVISIBLE TIMES)
and a few other invisible math operators around U+2062. I think the best
to do for them is to put invisible glyph (zero-contour, non-advancing
or a very small width) for them by default and to have GSUB lookups to
be turned on by 'font clients' in case it's desriable/required that
they be rendered with visible glyphs. That way, 'naive' clients of
the fonts would not render invisible characters with visible glyphs
unknowingly. By 'naive', I mean passing a Unicode string containing
U+2062-like characters without preprocessing (e.g. removing them )
to a string-drawing API.
Jungshik
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