Saturday, April 05, 2008

10 common errors when implementing accessibility

What not to do for accessibility ...

Web developers attempting to build accessible websites often make the same mistakes time and time again. Although they're trying their hardest sometimes their overzealousness gets in the way and actually hinders the accessibility of their websites.

The below 10 guidelines tell you what not to do, so you too don't fall foul to these same common accessibility errors...

1. Don't use verbose ALT text

Accessible web developers often insert far too much ALT text on to images, in the hope that this will help screen reader users. ALT text for information-based images should be short and succinct, and contain no more and no less information than what's in the image.

Decorative images should always be given null ALT text, or alt="", so that they're ignored by screen readers. Assigning ALT text that adds no real value makes it harder for screen reader users to work through the page as so much unnecessary content is being sent in their direction.

2. Don't use random characters to separate links

One of the more minor accessibility guidelines states that adjacent links should be separated with non-link text. The reason this guideline exists is that some very old web browsers had problems with adjacent links, whereby they ended up making all adjacent links point to the same page.

This guideline is no longer relevant but can often cause accessible web developers to insert invisible characters (usually vertical bars) in between links. Unfortunately, each vertical bar is announced to screen reader users as ‘vertical bar’, which is of course nonsensical and makes it harder for these users to work through the page.

3. Don't insert text into empty form fields for the sake of it

Another old and outdated guideline states that any empty form field should have placeholding text inside of it. This guideline originally existed as very old screen readers weren't always able to pick up empty form fields.

All major screen readers now pick up empty form fields (and have done so for some time now) so it's safe to ignore this guideline and not insert pointless text into a form field. Indeed, screen readers often don't announce this placeholding text so screen reader users may enter their text in addition to the placeholding text without realising it.

4. Don't use access keys

You can assign access keys to any links or form items so as to provide keyboard shortcuts to them. In theory this sounds like a great idea as screen reader and keyboard-only users should easily be able to activate key links from anywhere on any page.

Access keys shouldn't however be used as they can override keyboard shortcuts for screen readers, rendering key screen reader functionality useless. The other problem with access keys is there's no convention so the few sites that use them do so in whichever way they choose. Site visitors are unlikely to spend the time getting accustomed to your website's particular access keys.

5. Don't use the table summary (unless it actually adds value)

The table summary can be inserted on to any HTML table and is essentially a summary of what the table is. Screen readers read aloud table summaries before reading through the table, providing them with a summary of the table content prior to listening to the whole table.

The table summary should always be omitted from a layout table. Websites using a tabular layout sometimes have table summaries of ‘layout table’ which of course add no value at all.

Even with data tables, a table summary is only needed if there's insufficient information provided about the table on the page (which isn't usually the case)."    (Continued via Webcredible)    [Usability Resources]

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