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RE: US-ASCII characters versus XML characters ... whysuch a h

• From: Amelia A Lewis <amyzing@talsever.com>
• To: xml-dev@lists.xml.org
• Date: Mon, 1 Oct 2012 11:16:47 -0400

On Mon, 1 Oct 2012 14:47:15 +0000, Costello, Roger L. wrote:
> David Carlisle wrote:
> 
>>> 1. Why does XML not support many of the US-ASCII characters?
>>> 
>> Because it's a textual format and code points like
>> U+0017 END OF TRANSMISSION BLOCK
>> don't really belong in text.
> 
> Not everyone agrees with that point of view.

They're wrong, or they're speaking less formally than they ought.

> For example, RFC 5322 
> [1], Internet Message Format, is for *text* document and it says:
> 
>       This document specifies the Internet Message Format (IMF), 
>       a syntax for *text* messages that are sent between computer 
>       users, within the framework of "electronic mail" messages.
> 
>       This document specifies a syntax only for *text* messages.  In
>       particular, it makes no provision for the transmission of images,
>       audio, or other sorts of structured data in electronic mail messages.
> 
>       A message that is conformant with this specification is composed of
>       characters with values in the range of 1 through 127 and interpreted
>       as US-ASCII [ANSI.X3-4.1986] characters.
> 
> So, according to this RFC "U+0017 END OF TRANSMISSION BLOCK" does 
> belong in text (as do all the other 27 US-ASCII characters that XML 
> does not support).

I recommend that you attempt to send a message containing the second 
through thirty-second characters (1-31) to a random selection of MTAs, 
and see what happens. Try putting them in the body, one per line. Try 
putting them in headers. See how many get through, and how consistent 
transmission actually is. Treatment of 0x08 (BS) can be particularly 
amusing.

Then see what displays in a random selection of MUAs (after verifying 
what's been lost in transmission).

Internet Message Format permits these things because it's a legacy from 
RFC822 (and even before). It's unwise to use them.

Amy!
-- 
Amelia A. Lewis                    amyzing {at} talsever.com
Yankees are compelled by some mysterious force to imitate Southern 
accents and they're so damn dumb they don't know the difference between
a Tennessee drawl and a Charleston clip.
                -- Rita Mae Brown, "Rubyfruit Jungle"

• References:
  • US-ASCII characters versus XML characters ... why such a hugediscrepancy?
    • From: "Costello, Roger L." <costello@mitre.org>
  • Re: US-ASCII characters versus XML characters ... whysuch a huge discrepancy?
    • From: David Carlisle <davidc@nag.co.uk>
  • RE: US-ASCII characters versus XML characters ... whysuch a huge discrepancy?
    • From: "Costello, Roger L." <costello@mitre.org>