From: James Kass (email@example.com)
Date: Thu Oct 11 2007 - 00:27:58 CDT
> Q: How should characters be displayed if the rendering system
> doesn't fully support them?
The correct answer is that it depends on the operating system and the
font(s) in use. Display issues such as these are beyond the scope of a character encoding standard. Suggestions are fine, defining expected
behavior is not.
> A: There are three main options, depending on the type of
> character involved. Some should not display at all (zero-width
> invisible characters); some should display as a visible (but blank)
> space; and some should be displayed with one or more generic
> glyphs, often referred to as "missing glyphs" or a ".notdef glyph".
The appearance of the "missing glyph" in a font is completely under
the control of the font developer. Many developers use a hollow
rectangle, but some developers use their own logos. Even some
mainstream fonts, like MingLiU, have a spacing glyph with no
contours for the missing glyph. (No contours means that, in
such fonts, the missing glyph will display as a space. Take any
blank sheet of paper, it matches MingLiU's display of any Canadian
Syllabics text, for instance.)
> Where a font is being designed for a rendering system that does
> not handle invisible characters (such as variation selectors), then
> the best glyph for them — in the absence of other support — is a
> zero-width invisible glyph.
Fonts are built to the font specs and should be cross-platform. In
the unlikely event that a developer targets a rendering system which
doesn't handle so-called invisible characters, the font developer has
a slim chance of knowing if and when the rendering system might
be updated. Savvy font developers hew to the line, and let the chips
fall where they may.
The attached graphic "2229VS1.GIF" shows the display of the same
text in two different fonts. What do the authors of this FAQ
consider "broken" in this picture? One font? Both fonts? The
operating system? The rendering system? The application?
The correct answer is that the operating system, both the fonts,
the rendering system, and the application are behaving correctly
and as expected.
Here's the text string used in the graphic: ∩ + ︀ = ∩︀
P.S. - I doubt if 'how to display unsupported characters' is really
asked frequently and wonder what criteria determines the
frequency of FAQs on the Unicode site. If it *is* a FAQ, then
it should be asked on the OpenType list rather than at the
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