[NNTP] Command names

[Clive D.W. Feather]

Splitting this out as a sub-thread:

Ken Murchison said:
> Clive D.W. Feather wrote:
>> At present a command name is not restricted in any way (other than no
>> spaces). I wonder if it would be a good idea to limit both extension labels
>> and command names to some smaller character set (say alphanumeric plus dot
>> and dash)? Do we want to forbid commands like "401" or "!@%)$&:#". Or, even
>> worse, names with quotes? Whatever we decide, I think that we should use
>> the same rule for extension labels and command names.
> Yes, I could see allowing alphanumeric plus a few other special chars, 
> and probably force the first char to be alpha.

Okay, here's the proposal. Any comments or objections?

In 3.1:

- Keywords MUST consist of printable US-ASCII characters.
+ Keywords MUST contain only US-ASCII letters, digits, dot ("." or %x2E),
+ and dash ("-" or %x2D) and MUST begin with a letter.

[The bit about case-insensitive is further down.]

In 8:

- An extension is identified by a unique extension-label, which is a string
- of 1 to 12 uppercase US-ASCII letters.
+ An extension is identified by a unique extension-label, which is a
+ keyword; it MUST be between 3 and 12 characters, MUST contain only
+ US-ASCII letters, digits, dot ("." or %x2E), and dash ("-" or %x2D),
+ and MUST begin with a letter. Extension-labels are case insensitive.

In 9.1:

- x-command-name = 3*12A-CHAR
+ x-command-name = keyword

In 9.4:

- extension-label = 1*12UPPER
+ extension-label = keyword

In 9.5:

+ keyword = ALPHA 2*11(ALPHA / DIGIT / "." / "-")

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