Bad song lyric puns continue, with apologies to Alison Moyet ;).
21. Look for invisible keyboard focus when tabbing through a page.
First of all, what exactly is that? It means that we have spots on the page that do not allow us to select items or don't give us any indication as to where on the page we actually are.
Here's a quick example. Since I figure it's only fair to call out stuff that is mine or that I actively use, let's look at the TESTHEAD site again.
If we look at the first picture, we see that I have tabbed over the element that features the Twitter link. As you can see, it has a highlight around it to show the keyboard focus being over that element:
Let's press the tab three times so that we can highlight the G+ element:
Notice anything interesting? The G+ element has no highlight around it. Let's see what happens when we turn on VoiceOver:
VoiceOver creates its own keyboard focus element, and we see/hear the words stated when we are tabbing through the document. Turn off VoiceOver and there's no indication that G+ is selected. If we press Enter while we have tabbed to the G+ element, even if we don't see the highlight, the element is where the keyboard focus is, so pressing Enter brings up the G+ dialog.
There you go, a simple example. You might be saying "OK, but so what. Just turn your screen reader on and problem solved." Do you want to have a screen reader on all the time? If you aren't a person with low vision but have a motor disability, do you want to hear that voice all the time? More to the point, what if you look away for a bit and need to get back to the keyboard, do you know where you are? Sure, you can Shift+Tab and then Tab again to get back to where you are (a process I do very frequently for this very purpose), but it's not something I look forward to. Plain and simple, if we have an option to highlight where we are on the page, do so. If something doesn't get highlighted that should be, raise attention to that fact.