These are status reports from the server and indicate the response to
   the last command received from the client.

   Status response lines begin with a 3 digit numeric code which is
   sufficient to distinguish all responses.  Some of these may herald
   the subsequent transmission of text.

   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.

   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
      x8x - Nonstandard (private implementation) extensions
      x9x - Debugging output

   The exact response codes that should be expected from each command
   are detailed in the description of that command.  In addition, below
   is listed a general set of response codes that may be received at any
   time.

   Certain status responses contain parameters such as numbers and
   names. The number and type of such parameters is fixed for each
   response code to simplify interpretation of the response.

   Parameters are separated from the numeric response code and from each
   other by a single space. All numeric parameters are decimal, and may
   have leading zeros. All string parameters begin after the separating
   space, and end before the following separating space or the CR-LF
   pair at the end of the line. (String parameters may not, therefore,
   contain 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 by a space.  Also, note that the text following a response
   number may vary in different implementations of the server. The
   3-digit numeric code 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 x8x specified above.  (Note
   that debugging is provided for explicitly in the x9x response codes.)
   The use of unspecified response codes for standard commands is
   prohibited.

   We have provided a response pattern x9x for debugging.  Since much
   debugging output may be classed as "informative messages", we would
   expect, therefore, that responses 190 through 199 would be used for
   various debugging outputs.  There is no requirement in this
   specification for debugging output, but if such is provided over the
   connected stream, it must use these response codes.  If appropriate
   to a specific implementation, other x9x codes may be used for
   debugging.  (An example might be to use e.g., 290 to acknowledge a
   remote debugging request.)