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FTSC                             FIDONET TECHNICAL STANDARDS COMMITTEE
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Publication:    FTA-1006
Revision:       2
Title:          Key words to indicate requirement levels
Author:         Administrator
Revision Date:  17 January 1998
Expiry Date:    17 January 2000
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Contents:
                1. MUST
                2. MUST NOT
                3. SHOULD
                4. SHOULD NOT
                5. MAY
                6. Guidance in the use of these imperatives
                7. Security considerations
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Status of this document
-----------------------

  This document is an FTSC Administrative document (FTA), and
  specifies a Fidonet Best Current Practice for the Fidonet community.
  Distribution of this document is unlimited.


Abstract
--------

  In many standards documents several words are used to signify the
  requirements in the specification. These words are often
  capitalized. This document defines these words as they should be
  interpreted in FTSC documents. Authors who follow these guidelines
  should incorporate this phrase near the beginning of their document:

    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
    NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL"
    in this document are to be interpreted as described in FTA-xxxx.

  Note that the force of these words is modified by the requirement
  level of the document in which they are used.

  The key words in *this* document itself are to be interpreted as
  described here.


1. MUST
-------

  This word, or the terms "REQUIRED" or "SHALL", mean that the
  definition is an absolute requirement of the specification.


2. MUST NOT
-----------

  This phrase, or the phrase "SHALL NOT", mean that the definition is
  an absolute prohibition of the specification.


3. SHOULD
---------

  This word, or the adjective "RECOMMENDED", mean that there may exist
  valid reasons in particular circumstances to ignore a particular
  item, but the full implications must be understood and carefully
  weighed before choosing a different course.


4. SHOULD NOT
-------------

  This phrase, or the phrase "NOT RECOMMENDED" mean that there may
  exist valid reasons in particular circumstances when the particular
  behavior is acceptable or even useful, but the full implications
  should be understood and the case carefully weighed before
  implementing any behavior described with this label.


5. MAY
------

  This word, or the adjective "OPTIONAL", mean that an item is truly
  optional. One vendor may choose to include the item because a
  particular marketplace requires it or because the vendor feels that
  it enhances the product while another vendor may omit the same item.
  An implementation which does not include a particular option MUST be
  prepared to interoperate with another implementation which does
  include the option, though perhaps with reduced functionality. In
  the same vein an implementation which does include a particular
  option MUST be prepared to interoperate with another implementation
  which does not include the option (except, of course, for the
  feature the option provides.)


6. Guidance in the use of these imperatives
-------------------------------------------

  Imperatives of the type defined in this document must be used with
  care and sparingly. In particular, they MUST only be used where it
  is actually required for interoperation or to limit behavior which
  has potential for causing harm. For example, they must not be used
  to try to impose a particular method on implementors where the
  method is not required for interoperability.


7. Security considerations
--------------------------

  These terms are frequently used to specify behavior with security
  implications. The effects on security of not implementing a MUST or
  SHOULD, or doing something the specification says MUST NOT or SHOULD
  NOT be done may be very subtle. Document authors should take the
  time to elaborate the security implications of not following
  recommendations or requirements as most implementors will not have
  had the benefit of the experience and discussion that produced the
  specification.


A. References
-------------

  [RFC2119] "Key words for use in RFCs to Indicate Requirement
  Levels". Scott Bradner. March 1997.


B. Acknowledgements
-------------------

  This document is heavily based on the original text of RFC2119 by
  Scott Bradner. Please read that document for further
  acknowledgements.


C. Author contact data
----------------------

  Odinn Sorensen
  Fidonet: 2:236/77
  E-mail:  odinn@goldware.dk
  WWW:     http://www.goldware.dk


D. History
----------

  Rev.1, 19971118: First release as draft.
  Rev.2, 19980117: First release as official FTA. Clarified whether
                   the document applies to itself (which it does).


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