Permissions Hierarchy - GRANT on logins/users/roles

A question on the permissions hierarchy:

Since logins, database users, and database roles are both principals and securables - what does it mean to GRANT permission on a login/user/role to another principal? Does it mean that for a login - you can GRANT permission to EXECUTE AS that login or modify it, for example?

Thanks!

Yes, you can grant IMPERSONATE to execute as that principal or ALTER/CONTROL to allow its modification.

Laurentiu|||Thanks again!