Accessibility in web design refers to inherent design features or other aids that assist disabled users. These features can include devices such as screen readers for the visually impaired, transcripts for those with auditory impairments and special devices for those with limited manual dexterity. Many of the strategies that improve accessibility are also generally beneficial to those who have limited experience or less than optimal connections. Accessible pages are also more effectively indexed by search engines.
There are four broad categories of impairment that you will want to consider.
People with low or no vision are going to have problems with text that is too small or which contrasts poorly with the background. They may also have problems with text that is all in italics or in a font face that is difficult to read. They may be using a screen reader, Braille display or a screen magnifier. Make use of the alt tag on any pictures you use. To test if your site “breaks” at higher magnifications, use the zoom setting on your browser.
If you have audio content on your website, you should also have transcripts.
Users with mobility impairments have a variety of devices they can use to navigate or enter information. The reason why this is important on the design end is that forms or other interactive features may be more difficult for people with mobility issues to use. (As an example, I have noticed that some online surveys and other forms “jump,” making it very difficult to make a correct selection.)
Some examples of cognitive impairments include attention problems, reading and problem solving impairments and memory issues. Sites should be designed simply and distracting elements should be removed or reduced.