From the Anchorage Daily News: Wow, there are so many things to consider if you want your Web site to be truly accessible to everyone. From the story: "Common failings include:

Audio streams that convey critical information but are unaccompanied by a text equivalent for the deaf or hard of hearing.

Type and background colors with too little contrast to be distinguished by the colorblind. (This can affect up to one in 12 visitors to a Web site.)

Flickering or flashing animations that at certain frequencies can trigger convulsions in susceptible individuals.

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Incompatiblities with Apple computers or with less-common browser software, or failure to adapt pages to text-only devices.

Text presented as a scanned image, making it invisible to the automated text readers used by the blind. (Web designers can attach explanatory notes known as "alt" tags to distinguish meaningless "blank" images like corners and spacers from meaningful images like "image of bear biting salmon's head off.")"