anchor.diff:  
       rule return_statement:
           TOKRETURN assign_rvalue SEMICOLON
  -
  -    rule group_statement:
  -        TOKBEGIN
  -        statement_list
  -        TOKEND
  -
  -    rule seq_statement:
  -        TOKSEQ
  -        statement_list
  -        TOKENDSEQ
  -
  -    rule action_statement:
  -        TOKACTIONSTATEMENT [ COLON  VAR] [ SEMICOLON ]
  -        statement_list
  -        TOKENDACTION [ COLON VAR]
  -
  -    rule actionvalue_statement:
  -        TOKACTIONVALUESTATEMENT
  -        statement_list
  -        TOKENDACTIONVALUE
   
       rule case_statement:
           TOKCASE paren_expression
  
positive.code: 
      rule method_declaration:
          TOKMETHOD 
          type_decl [ VAR ] [ formal_list ]
          #( builtin_type VAR [ formal_list ]
          #| VAR [ VAR ] [ formal_list [ VAR ] ]
          #)
  
negative.code:         )*
  
      rule assign_rvalue:
          ( group_statement
          | case_statement
          | interface_declaration
          | TOKRULES [ COLON  VAR]
              ( rule_statement )*
  