Re: C1 Control Pictures Proposal

From: Ken Whistler <>
Date: Wed, 17 Aug 2011 14:49:46 -0700

In general, I agree with Doug Ewell's assessment. I don't see a convincing
case here for the need to encode more control picture characters for C1
controls. There seems to be a confusion here between the need for
glyphs and the need for characters. Also, this would seem to me to
be a receding horizon kind of problem. The same arguments could be
(and have been) claimed for Unicode format controls, which also don't
have visible displays of their own.

Further comments:

On 8/13/2011 10:48 AM, Sean Leonard wrote:
> In accordance with this and other text in the Standard, it is not really possible to assign glyphs uniformly and interchangeably to the code points in U+0000-U+001F and U+0080-U+009F.

Of course it is. The Unicode Standard has done so for years: they are
called code chart
display glyphs. What one cannot expect is that plain text renderers will
display control
characters as visible glyphs in a uniform fashion -- they aren't
supposed to, because
the control codes aren't graphic characters. That is,rather, what "show
hidden" modes
are all about, and there really aren't any constraints on the details of
exactly how
a show hidden implementation may choose to display the undisplayable, as
it were.

> Variation selectors (sec. 16.4), for example, "provide a mechanism for specifying a restriction on the set of glyphs that are used to represent a particular character [examples given of CJK ideographs and Mongolian letters]." Variation selectors and other Unicode-defined control code points are ill-suited to causing C1 values to be displayed, because C1 values have no "display representation" in and of themselves.

That whole discussion of variation selectors is beside the point.
Variation sequences can
only be defined for *base* characters. Base characters are a subset of
characters (see D51 in Chapter 3 of the Unicode Standard). Control
aren't graphic characters. Hence they are not base characters, either,
and could
never be used in variation sequences, anyway.

Received on Wed Aug 17 2011 - 16:52:09 CDT

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