The commercial website YoyoDesign has good information about creating a handicapped-accessible website. I encourage to read the entire page, but here are the opening paragraphs:

People who have a medical condition or disability don’t always have the same online experience as someone who doesn’t.

But what can be done to help people in this position? And what sanctions are currently in place to ensure everyone is included? Let’s get a better understanding of website accessibility as a whole.

What is website accessibility and why do you need it?

Website accessibility is the practice of creating a web page that can be used by anyone, regardless of their ability or condition.

Accessibility ensures a person will be able to perceive, navigate, and even contribute to the web. There are a number of disabilities which fall into the bracket of needing website accessibility assistance. Some of the most prevalent include:

Auditory
These are issues with hearing audio footage. This is a particular problem on websites that primarily use video content.

Cognitive
This is when someone has a mental condition that prevents them from fully understanding what they’re reading.

Visual
Having a visual impairment makes it incredibly tough to use the internet. After all, the majority of content is created with the able-sighted in mind.

Neurological
These are diseases caused by the brain which result in you having limited control over your nervous system. Parkinson’s is arguably the most notable example of this.

Speech
The inability to properly communicate could cause problems in an age where voice commands are becoming increasingly popular.