ietf-nntp Response codes - debugging, authentication & unknown

[Lee Kindness]

I've put together my opinions into a reworded section 4.1, changes and 
additions are marked by '!':

     4.1 Response Codes

       Each response MUST begin with a three-digit status indicator.
       These are status reports from the server and indicate the
       response to the last command received from the client.

       The first digit of the response broadly indicates the success,
       failure, or progress of the previous command.

       1xx - Informative message
       2xx - Command ok
       3xx - Command ok so far, send the rest of it.
       4xx - Command was correct, but couldn't be performed for some
             reason.
       5xx - Command unimplemented, or incorrect, or a serious
             program error occurred.
!      9xx - Reserved for a possible future debugging extension.

       The next digit in the code indicates the function response
       category.

       x0x - Connection, setup, and miscellaneous messages
       x1x - Newsgroup selection
       x2x - Article selection
       x3x - Distribution functions
       x4x - Posting
!      x7x - Nonstandard (private implementation) extensions
!      x8x - Authentication
!      x9x - Private debugging output

       The exact response codes that can be returned in response to a
       given command are detailed in the description of the keyword
!      that is the first part of the command. If a client receives
!      an unexpected response code from a command then it MUST make
!      a 'best guess' on how to treat the response - typically the
!      first digit is used for this purpose.

       Certain response codes contain parameters such as numbers and
       names in addition to the status indicator. In those cases, the
       number and type of such parameters MUST be fixed for each
       response code to simplify interpretation of the response. In
       all other cases, the client MUST only use the status indicator
       itself to determine the nature of the response.

       Parameters MUST be separated from the numeric status indicator
       and from each other by a single US-ASCII space. All numeric
       parameters MUST be in base 10 (decimal) format, and MAY have
       leading zeros. All string parameters MUST begin after the
       separating space, and MUST end before the following separating
       space or the US-ASCII CRLF pair at the end of the line.
       (Therefore, string parameters MUST NOT contain US-ASCII
       spaces.) All text, if any, in the response which is not a
       parameter of the response must follow and be separated from
!      the last parameter, or respose code, by an US-ASCII space.
       Also, note that the text following a response number may vary
       in different implementations of the server. The 3-digit numeric
       status indicator should be used to determine what response was
       sent.

       Response codes not specified in this standard MAY be used for
       any installation-specific additional commands also not
!      specified. These SHOULD be chosen to fit the pattern of x7x
!      specified above.

       The use of unspecified response codes for a standard command
       is prohibited.

!      The status indicator pattern x9x is provided for private
!      debugging. The use of these responses is out of the scope
!      of this standard. Deployed servers MUST NOT present
!      debugging responses to clients without prior arrangement.

       A server MUST respond to an unrecognized, unimplemented, or
       syntactically invalid command with a negative response code
       (status indicators of the form 5xx).  For unrecognized
       commands, the 500 response code MUST be returned. This
       includes servers that have not implemented the optional
       extensions outlined later in this memo. For recognized
       commands where the syntax is wrong, the 501 response code MUST
       be returned. A server MUST respond to a command issued when
       the session is in an incorrect state by responding with a
       negative status indicator. This may be from either the 4xx or
       5xx group as appropriate.

Comments are welcomed.

-- 
 Lee Kindness