anchor.diff:      ;
   
   alternative
  -    : term ( '|' term)*
  +    : term ( BAR term)*
       ;
   
   term
  
positive.code: 
  ID
      : '<' .*? '>'+
      ;
  
  TEXT
  
negative.code:     ;
  
  optional
      : REND alternative+ LEND
      ;
  
  zeroormore
      : RBRACE alternative+ LBRACE
      ;
  
  oneormore
      : RPAREN alternative+ LPAREN
      ;
  
  text
  