[NNTP] Capability modifiers

[Clive D.W. Feather]

Okay, this remains the one contentious issue. I'd like us to get it closed
off because we'd all like to see the draft out.

I initially proposed them so that we wouldn't get stuck if we ever need to
extend the syntax of capabilities. The minimal requirements are:
* servers: none.
* clients: MAY completely ignore lines with modifiers completely,
           MUST NOT crash.

I then proposed the modifiers beginning with dash to mean "not available
for reason X":

  --      cannot be re-enabled
  -480    requires authentication
  -483    requires privacy protection
  -label  requires something related to the capability with that label

Other people suggested some wording and concept cleanups; in particular,
two modifiers on a line is an "and" while multiple lines is an "or".

-MODE-READER is seeing actual use elsewhere in the draft; specifically
    -MODE-READER READER
indicates that reader commands will be available after MODE READER.

Russ sees little or no point in the concept and, more specifically, the
-480 and -483 cases. If I'm understanding his point, he's saying that
authentication or privacy setup might fail anyway (e.g. wrong credentials
for the desired operation) and so these provide little or no information
except in edge cases.

I'm not sure where we go from here.

If we remove modifiers entirely, we still want to say *something* about
extensibility of the CAPABILITIES syntax, and we still need something to
replace the -MODE-READER modifier in particular.

So, some questions for people:

* Is the modifier *concept* worth retaining as a hook for syntax extension?
If not, how do we address that?

* Is the -- modifier useful as a documentation technique?

* Is the -label modifier useful for interrelated capabilities?

* Are the -480 and -483 modifiers useful for indicating what is and
isn't available with and without security and privacy?

* If we remove modifiers, what do we do about -MODE-READER?

-- 
Clive D.W. Feather  | Work:  <clive at demon.net>   | Tel:    +44 20 8495 6138
Internet Expert     | Home:  <clive at davros.org>  | Fax:    +44 870 051 9937
Demon Internet      | WWW: http://www.davros.org | Mobile: +44 7973 377646
Thus plc            |                            |