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BNF

   metasyntactic notation used to specify the syntax of programming
   languages, command sets, and the like.  Widely used for language
   descriptions but seldom documented anywhere, so that it must
   usually be learned by osmosis from other hackers.  Consider this
   BNF for a U.S. postal address:


      <postal-address> ::= <name-part> <street-address> <zip-part>


      <personal-part> ::= <name> | <initial> "."


      <name-part> ::= <personal-part> <last-name> [<jr-part>] <EOL>
                    | <personal-part> <name-part>


      <street-address> ::= [<apt>] <house-num> <street-name> <EOL>


      <zip-part> ::= <town-name> "," <state-code> <ZIP-code> <EOL>


   This translates into English as: "A postal-address consists of a
   name-part, followed by a street-address part, followed by a
   zip-code part.  A personal-part consists of either a first name or
   an initial followed by a dot.  A name-part consists of either: a
   personal-part followed by a last name followed by an optional
   `jr-part' (Jr., Sr., or dynastic number) and end-of-line, or a
   personal part followed by a name part (this rule illustrates the
   use of recursion in BNFs, covering the case of people who use
   multiple first and middle names and/or initials).  A street address
   consists of an optional apartment specifier, followed by a street
   number, followed by a street name.  A zip-part consists of a
   town-name, followed by a comma, followed by a state code, followed
   by a ZIP-code followed by an end-of-line."  Note that many things
   (such as the format of a personal-part, apartment specifier, or
   ZIP-code) are left unspecified.  These are presumed to be obvious
   from context or detailed somewhere nearby.  See also parse.
   2. Any of a number number of variants and extensions of BNF proper,
   possibly containing some or all of the regexp wildcards such
   as `*' or `+'.  In fact the example above isn't the pure
   form invented for the Algol-60 report; it uses `[]', which was
   introduced a few years later in IBM's PL/I definition but is now
   universally recognized.  3. In science-fiction fandom, a
   `Big-Name Fan' (someone famous or notorious).  Years ago a fan
   started handing out black-on-green BNF buttons at SF conventions;
   this confused the hacker contingent terribly.