No one can tell someone how they "HAVE" to make their website, but webmasters and website designers usually stick to regulations and some standards that are made to help visually impaired Internet users so that visitors are willing to use their website.
A good website needs to promote disabled and visually impaired activity by adding certain tools and widgets to make a site more accessible. Many websites throughout the Internet do this already, but many do not, and visually impaired users still do have trouble while surfing the Internet. Visual Impairment is something that will remain an issue or topic on the web for a long time, and many more websites are starting to use different tools to make the Internet better for visually impaired users of the Internet.
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For more information about Web Standards visit http://w3.org
