gistfile1.txt

// BB_WORD: a valid tag name; essentially a string literal terminated by whitespace or a reserved character
// TEXT: non-BBCode text (i.e. string literal)
// BB_VAL: A string literal inside a BBCode tag
// e.g. [img src="foo"] matches [BB_WORD BB_WORD=BB_VAL]

Stmts -> Stmt Stmts
       | ε

Stmt -> TEXT
      | Tag

Tag -> OpenTag Stmts CloseTag
     | SelfClosingTag

OpenTag -> [ TagContents ]

CloseTag -> [ / BB_WORD ]

SelfClosingTag -> [ TagContents / ]

TagContents -> BB_WORD TagArgs
             | BB_WORD

TagArgs -> TagArg TagArgs
         | ε

TagArg -> BB_WORD = ArgValue

ArgValue -> BB_WORD
          | NUMBER
          | STRING

// BB_WORD: a valid tag name
// TEXT: non-BBCode text (i.e. string literal)
// BB_VAL: A string literal inside a BBCode tag
// e.g. [img src="foo"] matches [BB_WORD BB_WORD=BB_VAL]
// Note: this grammar is not suitable for top down parsing
//       it needs to be right recursive and be left factored

Stmts -> Stmts Stmt
       | Stmt

Stmt -> TEXT
      | Tag

Tag -> OpenTag Stmts CloseTag
     | SelfClosingTag

OpenTag -> [ TagContents ]

CloseTag -> [ / BB_WORD ]

SelfClosingTag -> [ TagContents / ]

TagContents -> BB_WORD TagArgs
             | BB_WORD

TagArgs -> TagArgs TagArg
         | TagArg

TagArg -> BB_WORD = ArgValue

ArgValue -> BB_WORD
          | NUMBER
          | STRING