Re: ASCII (was Run Script upon Waking? Solved!)
Re: ASCII (was Run Script upon Waking? Solved!)
- Subject: Re: ASCII (was Run Script upon Waking? Solved!)
- From: Chris Nebel <email@hidden>
- Date: Sun, 02 Dec 2001 15:51:22 -0800
- Organization: Apple Computer, Inc.
"Bob.Kalbaugh" wrote:
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I'm not sure how to interpret this definition from the
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Tex-Edit Plus Help Guide:
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------
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ASCII...
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0-31 (low ASCII) -- Control characters such as carriage return, tab,
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formfeed and linefeed.
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32-127 -- Standard English characters, numbers and symbols.
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128-255 (high ASCII) -- Special ornaments, curly quotes, accented letters
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with diacritical markings. These characters differ across various computer
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platforms.
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--End--
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Is this definition wrong? Misleading?
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Should I consider that the characters 128-255 that Tex-Edit displays are
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special entities exclusive to the Mac platform and not ASCII characters
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after all?
Strictly speaking, ASCII only defines characters with codes from 0 to 127. It
allows the eighth bit to be used for pretty much anything you feel like --
parity, highlighting, extra characters, etc. -- but doesn't specify anything.
As a result, people have been talking about "extended ASCII" and "high ASCII"
for so long that the idea that ASCII codes go up to 255 has become pretty well
entrenched [1, 2].
There are encodings that define codes 128-255, notably the ISO-8859 family, but
that's something else. Mac OS uses its own encoding (Mac Roman in your case)
which defines many of the same characters as ISO-8859-1, but in different
positions. Tex-Edit is still giving you useful information about what
characters are at what code points, but it's not really ASCII.
--Chris Nebel
AppleScript Engineering
[1] In other words, you're in wide company, so this doesn't qualify as an ID10T
error. (I had to look that one up.)
[2] I got all this from <
http://czyborra.com/charsets/iso646.html> and
<
http://czyborra.com/charsets/iso8859.html>. Scary stuff in places -- makes you
appreciate Unicode.