事务中的mysql外键更新约束？

I can not find official mysql explanation about this, so I wanna throw it here. If I have foreign key constrains between two tables in MySQL, say tableA is the parent table, tableB is the child table. And, on parent tableA, I will use "ON UPDATE CASCADE ON DELETE CASCADE" to make sure actions of update/delete can be applied to child tableB by MySQL automatically.I can not find official mysql explanation about