anchor.diff:     ;
   
   line
  -   : lbl? (assemblerdirective | instruction)? comment?
  +   : lbl? (assemblerdirective | instruction) comment?
      ;
   
   instruction
  
positive.code: 
  
  REGISTER
     : A X | B C | C X | D X | C I | D I | B P | S P | I P | C S | D S | E S | S S
     ;
  
  
  
negative.code:    | OFFSET expression
     ;
  
  register
     : REGISTER
     ;
  
  string
     : STRING
     ;
  