Mobility impaired keyboard users rely heavily on highlighted links. A keyboard user will typically tab through link items and hit "enter" to activate the link. For this to work, the keyboard user needs to know where the current focus is, otherwise they have little hope of knowing where the next tab will take them. Site design can make this problem much worse if the links are on a background that make the dotted line difficult to detect. Mark Pilgrim is considering developing a more prominent focus indicator for Firefox, which would be a huge help if they can get the colour right.
The default link highlighting for the BBC website works fairly well (extra points for adding access key help in the tab sequence), but other websites such as CNN have a design that can be really tricky to navigate if you're using the tab key, particularly if your sight is less than perfect.
Stephen from Shaw Trust is a keyboard-only web user and he sometimes needs a little extra help to see links, particularly if the background to the link is a colour(particularly mid-grey) that makes the dotted line harder to see. Stephen has Cerebral Palsy which means that he finds it hard to focus on small areas of the screen. Highlighting a link (ala Salford University) makes the focus more prominent, and Stephen can get around the site much more easily. Mobility impairment combined with less-than-perfect vision is fairly common and will become more so as the average computer user gets older.
While offset links are a pretty good idea in lots of circumstances, don't forget that keyboard-only users don't have the benefit of having a screen reader. Therefore offset links such as "skip to content" need to be made visible so that sighted keyboard users also have the option of using them. BBC again does a good job of bringing offset links back on screen for this reason, and you can see another example of this technique used at the Salford University website.
If you're going to use this type of menu system then make sure that the hidden links are visible on focus so it's keyboard-user friendly.
SummaryThis all really boils down to two things:
- Make sure that all links are visible when they receive focus
- Create links that highlight when they recieve focus
Simple really, but not as well used as it ought to be.
Mike Cherim sent a link to an article he wrote a little while back detailing the technique used to achieve the highlighting effect: Let's Focus on Focus. It should be a fairly simple mod to make the script bring offset links back on screen. Cheers Mike!