Is this an error in SQL Server's documentation for ROLLBACK?

This is the SQL Server's document talking about the ROLLBACK statement. On that page it states that the syntax of it is as follows: ROLLBACK { TRAN | TRANSACTION } [ transaction_name | @tran_name_variable | savepoint_name | @savepoint_variable ] [ ; ] Apparently the stuff inside square brackets are optional and it seems you should choose one from TRAN or TRASACTION. But in fact you can completely omit both and ROLLBACK is a perfectly valid statement. Is this an error or intentionally?