    [NAME]
    ALL.dao.grammar.notation

    [TITLE]
    Grammar Notations

    [DESCRIPTION]

    Syntax definition: A ::= B, A is defined as B , which can be a descriptive sentence or
    a combination of the following definition items,
      1. Token: 'token'
      2. Descriptive: "description"
      3. Alternative: S | Y
      4. Optional: [ S ]
      5. Grouping: ( S )
      6. Repeating: S * or S +
           *  * : zero or more times;
           *  + : once or more times;
         For convenience, { S } is also used to represent repeating of S for zero or more
         times.

    Examples,
      *  ( S | Y )+ represents all the possible sequences composed of S and Y, such as: S; Y
         ; SY; YS; SSY ...
      *  S ( Y | N ) T represents: S Y T or S N T