Documentation: MySQL :: MySQL 5.1 Reference Manual :: 13.6.4.4 FOREIGN KEY Constraints

NO ACTION: In standard SQL, NO ACTION means no action in the sense that an attempt to delete or update a primary key value is not allowed to proceed if there is a related foreign key value in the referenced table. InnoDB rejects the delete or update operation for the parent table.

RESTRICT: Rejects the delete or update operation for the parent table. Specifying RESTRICT (or NO ACTION) is the same as omitting the ON DELETE or ON UPDATE clause. (Some database systems have deferred checks, and NO ACTION is a deferred check. In MySQL, foreign key constraints are checked immediately, so NO ACTION is the same as RESTRICT.)
English isn't my national language so maybe I didn't understand this text because I understand that in mysql NO ACTION = RESTRICT - if yes, why we have two the same things ?