Accessibility

Equivalency is the goal [...] Non-disabled people view the media landscape and take it all in, and so do disabled people; the fact that the view and the media landscape might differ for each camp is neither here nor there. Joe Clark

Accessible webpage designs are simple and clear. Everyone loves simple, clear webpages.

Five top tips

Use a decent text size that the user can make bigger or smaller with good foreground/background contrast. Even a modest visual impairment can make webpages hard to read. Anyone with less than 20/20 vision will benefit.
Include a meaningful text description for images. This is called ALT text.
Create links that are meaningful on their own. Assistive technology users (along with many non-disabled laptop users) - tab though links to find content they wish to read.
Mark up content for structure. Identify headings properly (it's not important how these are treated visually but that they are included) and include other content in paragraphs and lists - for the same reason as links.
Forms: keep it simple.

Improving accessibility is often about overcoming the limitations of serial access to content

A web page is like a long sausage of data. Visual browsers, like Internet Explorer, Safari, break this up into chunks and make it into something like a page. If you can see the page you can look up, down, left, right, hop about from bit to bit. You have random access to the page. Non-visual browsing, like text-to-speech output, means you have to hear the first bit first, then the next bit. This is serial access to the page.

Non-visual browsers are more sophisticated than telephone answering machines, though. They can make use of the structure of the page to provide quicker access to content. This means finding and pointing out headings, links, lists etc etc. A well-structured page is immensely helpful to many disabled users. Good structured mark-up for your content is probably the most helpul thing you can do to make your web pages accessible.

Improving accessibility is often about overcoming the limitations of using a mouse

The problem is not always obvious. A wheelchair use may have no trouble pulling up to her PC in her for a good browse. But someone who has arthritis in both hands may find he's denied access to many websites that require a mouse to activate menus used for navigation, or has links that are too close together.

Structure is important

Web pages without any structure are just blobs of text gobbed up on the screen, however prettily done. Prettiness provides definition for screen display but better is putting in some headings . These form a handy summary of the pagefor non-screen browsing and helps screen users work out what's what and search engines like them.

Images

Images are essentially for looking at with your eyes. Images help people who have difficulty with words or understanding long blocks of text. Unless a text alternative is offered people who can't see the images lose the information they carry which is often rich and rewarding.

Text

The majority of web content is text. Not all text is equal. Some is meant to stand out, like headings. People who can see the screen (or paper for that matter) can understand the difference from the visual presentation. People who use assistive technology that looks at the webpage structure to make sense of the content. If the text isn't marked up for structure (eg this is a heading, this is a list) making good sense of the page is hard, or impossible.

Text also cause difficulties when there's too much at once.

Tables

People with serial access to content suffer at the hands of tables. You need to understand the spatial arrangement of a table to make sense of it easily. In theory it is possible to mark up a table in an accessible way. Providing the information in an alternative format may be quicker to do and more useful to the end user.

A table can nearly always be presented as a list.

Forms

Because form input boxes are more or less the same, unless some kind of label is connected to each input box, users who can't read the whole form may get lost. If they stop browsing (say, for a cup of tea) and come back later, how do they know where they are? It's easy to review a form if you have random access (like can see it). Reviewing a form when you have serial access is hard. If the form is in a table (for good visual presentation) it may well be impossible to complete.

Text only and other goodies

It is easy to redisplay your website as text-only. This works if you have a logical page structure in the first place - otherwise, perhaps a mess, very revealing about well your designer has set out your web pages.

Text-only is not the holy grail of accessibility. It is helpful to some users. More important is concise, well-structured copy. Images convey alternative and additional information and excluding them may make life worse not better.

Checking for accessibility

If you want to test compliance, Ask Cynthia checks a webpage against accessibility guideline and points out (comprehensively) which elements do not follow one of two published standards. The US Section 508 standard is a basic starting point.

Meeting the 508 or other, longer standards doesn't guarantee your site is accessible to real disabled people (for example you could use a teeny-weeny text size and still pass).

The best way is to ask some disabled people to browse your website.