A sip-and-puff system is another type of alternative input device. It is controlled by a person's breath.
People who have a mobility disability might use assistive technology, such as a sip-and-puff input device or a pointing system that uses a cursor like the mouse.
Other people might be using a keyboard with no mouse, or a mouse with no keyboard, or neither. So it is important that people can read and move around your document however they are operating their computer.
As mentioned in the previous lesson, there are many things you can do when writing documents that will be read by people who are dependent on using different input and output devices.