I read something that made it seem as though InnoDB foreign keys can reference anything: primary keys, unique keys, and even non-unique columns...have I interpreted this correctly?

What do MySQL's other storage engines like MyISAM allow for what foreign keys can reference? Can they reference anything, or just primary keys, or primary keys as well as unique keys?

Thanks.

Foreign Keys defintions dont do anythingwork when using MyISAM
see the MySQL site for further details, and even then it depends on what version of MySQL you are using.

a Foreign Key constraint can only work on the referred (the "parent") table being unique keys which usually are also the primary key int he referred table.