Char James-Tanny opened by giving some statistics about disability, different types, how they can affect people of different ages.
But it isn't always possible to accommodate 100 percent of the people 100 percent of the time.
Many disabilities aren't visible. Many people with disabilities are online, for example in gaming. And no one knows they are disabled.
More benefits than just making documents and web pages accessible. It makes your content more searchable,
30 percent of mobile searches are for restaurants. And what do I want when I'm searching? Your location, your hours, and your menu.
Everything that is good for localization and translation is good for accessibility.
Interestingly, char talked about things such as formatting of content. But typographic consistency and alignment is important because dyslexics can have trouble reading otherwise.
Contrast is important. But the best contrast, black on white, can cause some people trouble when reading online. One solution is to make the background off-white. For example, instead of #FFF, try #FFD or #FFC.
If you want to test for colors, print in grayscale and see how much contrast you have. If you don't have any, that's what many color blind people will see.
Why are headings important? Screen readers can pull out headings. (Also why you don't want to use more than one h1 per page.)
It's important to understand that there are many types of disabilities, which include vision, hearing, speech, physical/motor, learning, psychiatric, cognitive, and intellectual.