anchor.diff:      :   'nonempty'
       ;
   
  -PRODUCE
  +/*PRODUCE
       :   'produce'
  -    ;
  +    ;*/
   
   RETURN
       :   'return'
  
positive.code:     | 'super' 
      | 'null'
      | 'none'
      | inlineClassDeclaration
      ;
  
  enumeration
  
negative.code: 
  directive
      : 'return' assignable? 
      //| 'produce' assignable
      | 'throw' expression? 
      | 'break' expression?
      ;
  