anchor.diff:  
       rule assign_rvalue:
           ( group_statement
  -        | case_statement
           | interface_declaration
           | TOKRULES [ COLON  VAR]
               ( rule_statement )*
  
positive.code:         [ formal_list ]
          [ provisos_clause ]
          ( equal_value SEMICOLON
          | SEMICOLON
              [
                  ( single_statement)+
                  TOKENDFUNCTION [ COLON  function_name]
              ]
          )
  
      rule import_arg:
  
negative.code:             )
          )+
  
      rule interface_contents:
            SEMICOLON [ interface_body ] TOKENDINTERFACE [ COLON VAR ]
          | equal_value
          | interface_body TOKENDINTERFACE [ COLON VAR ]
          | TOKENDINTERFACE [ COLON VAR ]
  
      rule interface_declaration:
          TOKINTERFACE CLASSVAR*
          ( typevar_item [SEMICOLON] [ interface_body ]
              TOKENDINTERFACE [ COLON VAR ]
          | interface_contents
          | VAR [ VAR ] interface_contents
          )
  
      rule function_declaration:
  