; This examples from WikiPedia <https://en.wikipedia.org/wiki/Backus%E2%80%93Naur_Form>.

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

        <name-part> ::= <personal-part> <last-name> <opt-suffix-part> <EOL>
                      | <personal-part> <name-part>

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

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

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

  <opt-suffix-part> ::= "Sr." | "Jr." | <roman-numeral> | ""
      <opt-apt-num> ::= <apt-num> | ""
