anchor.diff:      | TOKEN_RPAREN
       | TOKEN_LPAREN
       | TOKEN_QUESTION
  +    | TOKEN_MINUS
       | TOKEN_PLUS
       | TOKEN_STAR
       | TOKEN_BAR
  
positive.code:     | NONTERM_seq
      | NONTERM_seq_elem_list
      | NONTERM_seq_elem
      | NONTERM_predicate_opt
      | NONTERM_bound
      | NONTERM_patt
  
negative.code:   | RPAREN
    | LPAREN
    | QUESTION
    | MINUS
    | PLUS
    | STAR
    | BAR
  