From: Kent Karlsson (kentk@md.chalmers.se)
Date: Wed Jan 29 2003 - 12:51:46 EST
Keyur Shroff wrote
> Kent Karlsson <kentk@md.chalmers.se> wrote:
> >
> > A space followed by a dependent vowel sign should display just the
> > dependent vowel sign, no dotted circle. Indeed, (except for a "show
> > invisibles" mode, or a "character chart" display mode) no (Indic or
> > other)
> > text that does not contain the *character* DOTTED CIRCLE should ever
> > display a dotted circle as part of the displayed text. Systems that
> > do display a dotted circle (in normal display mode) where there is
> > no such *character* in the displayed text are buggy!
>
> In Indic scripts any sign that appear in text not in
> conjunction with a
> valid consonant base may be rendered with dotted circle as fallback
> mechanism (Section 5.14 "Rendering Nonspacing Marks"
> http://www.unicode.org/uni2book/ch05.pdf).
I don't know where you find support for that position in that text.
Can you please quote? There are no "invalid base consonants" for
any dependent vowel (for Indic scripts; similarly for any other script).
> Any system implementing this as
> default behaviour should not be considered buggy.
Indeed they are. And it should certainly not be default behaviour.
Any combining characters can be placed on any base characters without
there being any dotted circles displayed. In particular, any combining
Devanagari characters (note: including, in principle, several dependent
vowels, even if that does not occur in any (existing) orthography) can
be placed on any Devanagari base character as well as SPACE (and other
punctuation). What should result is a reasonable composed glyph, no
dotted circle in sight (except in show invisibles mode, which I'm not
discussing here). Spelling errors should be indicated otherwise, since
they are of a very different nature.
> For scripts other than Indic scripts, it may be useful to render the
> nonspacing mark without dotted circle because even after
> rendering it as an
> overlap glyph, the result is recognizable. However, for Indic
> scripts use
> of dotted circle is very useful as default behaviour since it gives
> immediate feedback to the user that there may be some
> defective combining
> character in the text. Most of the time such errors are unintentional
> rather than intentional.
No combination of base + combining characters is defective per se.
Even if the scripts are different within the combining sequence.
(Note also that the 0300 block of combining characters are script
independent.) Spelling errors is something else entirely.
> Unicode has provision to remove this dotted circle.
I'm not sure what you are talking about here.
> Space
> character is used
> to give indication to fallback mechanism that no dotted
> circle should be
> used while rendering this stand alone sign which is normally
> attached to
> other characters. This is useful when sometimes user want to
> display the
> sign without any circle. Also, with this scheme it is
> possible to show some
> combining marks with dotted circle and some without dotted circle.
The fallback mechanisms talked about in section 5.14 of TUS 3.0 is
the use of less than ideal (typographically!) mechanisms to display
an *approximation* of the glyph(s) for the combining sequence.
An exceedingly bad approximation is displaying a dotted circle as a
fake base (again: disregarding "show invisibles", or "chart" modes,
which, however, should be consistent and show a dotted circle fake
base for ALL combining characters occurring in the text). The use
of this exceedingly bad approximation (in normal display mode) does
in no way indicate that the combining sequence is at all defective.
It may indicate that the display engine (or the font) is defective...
/Kent K
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