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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:  [email protected]
 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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