anchor.diff:     ;
   
   atom
  -   : STRINGLITERAL
  -   | INTEGER
  +   : (STRINGLITERAL1 | STRINGLITERAL2 | INTEGER)
      | subject
      | command
      | '[' expression (',' expression)* ']'
  
positive.code:    ;
  
  pattern
     : STRINGLITERAL
     ;
  
  expression
  
negative.code: 
  
  COMMENT
     : '*' ~ [\r\n]*
     ;
  
  
  