Before revision: It serializes keystrokes; instead of pressing multiple keys at a time, the user is allowed to press and release a modifier key, such as , , , or the , and have it remain active until any other key is pressed.
After revision: It serializes keystrokes; instead of being required to press multiple keys at a time, the user can press and release a modifier key, such as , , , or the , and have it remain active until any other key is pressed.