InnoDB question

[Adam Sharp]

From what I've been reading in the MySQL documentation, 3.23.43b InnoDB features foreign
key constraints, which is great!
But from the MySQL 4.1 "wishlist" items found here (scroll to the bottom):
http://www.mysql.com/products/mysql-4.0/index.html
They mention hopes to support "foreign key integrity rules."
So maybe I'm showing my ignorance here, but I have to ask, what is the difference between
"foreign key constraints" and "foreign key integrity rules?"

Thanks,
Adam Sharp