ietf-nntp Wildmats

[Charles Lindsey]

In <20001116114737.L47729 at demon.net> "Clive D.W. Feather" <clive at demon.net> writes:

>In all except PAT, comma makes sense as alternative. If we provide a way to
>escape comma, then we can do the same for PAT and everything becomes much
>simpler to describe.

No, that is not the problem. It is the UNescaped commas that are going to
cause problems in PAT.

Suppose \S stands for "please match whitespace here". No, I am not
suggesting that as a notation, just to illustrate my argument for now.
Then, if PAT follows the current XPAT semantics, we get

	(X)PAT Subject 123- *foo bar*
meaning the same as
	(X)PAT Subject 123- *foo\Sbar*

But now look at
	(X)PAT Subject 123- *foo,bar bar,baz*
meaning the same as
	(X)PAT Subject 123- *foo,bar\Sbar,baz*

The first one looks like it is intended to match:
	Subject: foo bar
	Subject: foo baz
	Subject: bar bar
	Subject: bar baz
whereas the second one looks like it is intended to match
	Subject: foo
	Subject: bar bar
	Subject: baz

But they can't both be right :-( .

>> It does seem usual practice in other specs that backslashing things that
>> did not really need backslashing does the 'right thing'.

>Not quite: a *lot* of systems treat \<alpha> and \<digit> separately. But I
>agree with you for punctuation characters, which would include comma.

>I would suggest changing the wording so that:
>    \<punct>    escapes that punctuation
>    \<alpha>    undefined except as stated ) with the only example for now
>    \<digit>    undefined except as stated ) being \u if we include it

Yes, but usual practice seems to be
	"if \x has been given a special meaning, then use it;
	 otherwise \x means the same as x"
So that takes case of all \<alpha> and \<digit> cases, one way or the other.

But be careful also to make it clear that any special rule you write for
<alpha> or <digit> applies only to ASCII letters and digits, because in
UTF-8/Unicode as a whole there is no way to tell what is alpha/digit and
what is not. Or, putting it another way, only ever define \-escapes that
are readable as pure ASCII.

>-- 
>Clive D.W. Feather  | Work:  <clive at demon.net>   | Tel:  +44 20 8371 1138
>Internet Expert     | Home:  <clive at davros.org>  | Fax:  +44 20 8371 1037
>Demon Internet      | WWW: http://www.davros.org | DFax: +44 20 8371 4037
>Thus plc            |                            | Mobile: +44 7973 377646 

-- 
Charles H. Lindsey ---------At Home, doing my own thing------------------------
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