appropriateness of combination of controls (new suggestion)

["Kurt D. Zeilenga" <Kurt@OpenLDAP.org>]

I offer the following for WG consideration:

0)  Add to end of the first paragraph of 4.1.11.
 Implementations SHOULD only attach controls which are
 appropriate for the operation (as discussed in applicable
 specifications).

1) Insert new paragraph above the one which starts with
"The controlValue may contain information":

 When considering whether a control is appropriate for the
 operation, the implementation is not only to consider whether the
 control is attached to a message it was intended to be used
 with, but whether the control is being used appropriately
 in combination with other controls (of same or different
 controlType).

 When a server is faced with a sequence
 of controls which are not appropriate for the operation,
 the server may attempt, by ignoring any number of
 non-critical controls (including controls whose criticality
 field is to be ignored as discussed above), a sequence which
 is appropriate for the operation.  If such a sequence is found,
 the server is to make use of it when performing the
 operation.  Otherwise, servers are to fail the operation
 and, and for operations which have a response, indicate so by
 returning unavailableCriticalExtension (if any of the controls
 were marked critical) or protocolError (if the message is
 considered not well structured) or other appropriate result
 code.

 When a client is faced with a sequence of controls which
 are not appropriate for the operation, the client may
 attempt, by ignoring any number of controls, in order
 to make use of the response in its processing.  Alternatively,
 the client may treat the response as not well structured.

2) Remove the existing paragraph which starts with "Controls SHOULD NOT
be combined".

3) Replace as last bullet with:
	- optionally, semantics regarding combination of the
       control with other controls (of same or different
	controlType).  These semantics may rely on ordering
       of the controls in the sequence of controls attached
       to the message.

  It is noted that semantics of a combination of controls
  is generally found in the control specification most
  recently published.  In absence of a specification of
  a control combination semantics, implementors should
  generally regard use of the control in combination
  with other controls  as not appropriate for use in the same
  operation.  In presence of a specification which does not
  detail any order dependent semantics, the implementor is
  to regard the semantics as being independent on the
  order of controls.