Re: Too narrowly defined: DIVISION SIGN & COLON

From: Asmus Freytag <>
Date: Mon, 09 Jul 2012 19:32:47 -0700

There are many characters that are used in professional mathematical
typesetting (division slash being one of them) that need to be narrowly
distinguished from other, roughly similar characters. The point is that
these characters can be distinguished from each other when printed, and
that there's no readily available, general algorithm that could relieve
the user of having to specify the specific shape. (Thus making this
problem different from Arabic shaping and similar type of layout-driven
glyph selection).

Such narrowly defined characters are not aimed at the general user, and
it's totally irrelevant whether or not such a character ever becomes
"popular". In mathematics, these characters tend to be symbols (or
possibly punctuation), while linguistic notation has similar issues with
specialized letter shapes.

The reverse situation, where some characters are used for more than one
purpose, is different. Very early in the design cycle for Unicode there
was a request for encoding of a decimal period, in distinction to a full
stop. The problem here is that there is no visual distinction and the
function depends simply on the context in which the character is used
(it's the writer and reader who give the character its meaning).

Unicode has relatively consistently refused to duplicate encodings in
such circumstances, because the point about Unicode is not that one
should be able to encode information about the intent that goes beyond
what can be made visible by rendering the text. Instead, the point about
Unicode is to provide a way to unambiguously define enough of the text
so that it becomes "legible". How legible text is then "understood" is
another issue.

Because of that, there was never any discussion whether the ! would have
to be re-encoded as "factorial". It was not.

Now, to complicate matters, the early character sets did not make some
necessary distinctions. In normal printed text, one can easily
distinguish a minus sign from a hyphen, but in ASCII (and typewritten
text), that is not possible. Hence, the exceptional, and somewhat
awkward designation of the HYPHEN-MINUS character, which allows
coexistence with both an explicit HYPHEN and explicit MINUS character.
If Unicode had sprung directly from lead typography, there would be no
HYPHEN-MINUS, it's a carefully designed exception to deal with the fact
that way too much data exists where these have been conflated.

The European use (this is not limited to Scandinavia) of the division
symbol (a line with a dot above and below) and the colon (one dot above
the other) in the sense of minus sign and division sign clearly belongs
in the category of alternate use of existing characters. In other words,
it's like decimal point and factorial all over again. That this is the
correct way to view that particular issue is underscored by the fact
that one will be able to find both a regular minus sign and one that
looks like a division symbol used (in different contexts) in the same

Just as both the : and the / shapes can be found in the sense of
division. The last time I've seen the ":" was somewhere in my arithmetic
text books, but even there the fractions were using a slash (or a
horizontal line), there was no 1:4.

The proper thing to do would be to add these usages to the list of
examples of known contextually defined usages of punctuation characters,
they are common enough that it's worth pointing them out in order to
overcome a bit of the inherent bias from Anglo-Saxon usage.

Received on Mon Jul 09 2012 - 21:36:37 CDT

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