Keyboard access to a website is key to the usability of your site. All interactions and information that can be accessed with a mouse must be accessible with just a keyboard. This doesn't mean everyone who can't use a mouse will use a keyboard, but alternative AT inputs use keyboard-like inputs to navigate the web.
- Identify all interactions on the page.
- Using the tab, enter, and space bar, navigate the page and ensure each input and interaction can be triggered.
- Ensure rollover and hover interactions (help text, etc) can be triggered as well.
- If the user cannot interact with something, or get the information another way, this is a failure.
- Make sure the tab order of the page is logical and follows the visual order of elements on the page.
- If the tab order is confusing, this is a failure.
- Check that the focus is always visible when moving through the page with the tab key.
- If you lose focus, on a hidden link or other object when simply tabbing through the page, this is a failure.
- Make sure you can tab through the page and get back the address bar.
- If you ever need your mouse to get back to an element, this is a failure.
- Keyboard users must be able to easily use and dismiss modal dialog boxes, lightboxes, or other pop-ups.
- Modal dialog boxes need to trap the keyboard. When a modal dialog box is triggered, the keyboard focus needs to immediately move to the first actionable element in the modal.
- The keyboard cannot use the modal dialog box until it is dismissed. When a user moves the keyboard focus past the last element in the modal dialog box, it needs to loop to the beginning of the dialog box.
- The keyboard user needs to be able to access all controls in the dialog box, especially the controls to dismiss the dialog.
- If the keyboard user cannot do all of these things, this is a failure.
- Ideally, the keyboard user should also be able to dismiss the modal dialog box with the Escape key.
- If an interaction reveals hidden content.
- Ensure the focus is moved to the revealed content.
- If this does not happen, check for a programatic description of the change.
- Check for title tags providing information not on the screen.
- Title attributes which can only be exposed by hovering the mouse over the element are a failure of keyboard access.
- Check that the focus never goes to elements that won't be available to somebody using a mouse.
- If the keyboard focus goes to an offscreen element that has been temporarily hidden (items in a non-expanded drop-down menu, offscreen modals which haven't been triggered, etc.), this is a failure.
Avoid using tabindex of >= 1 as this will disrupt the normal tab order of the page. tabindex of -1 is only appropriate when autofocusing an element not normally interactive.
This is an example of a keyboard trap. Focus moves in a loop making the rest of the page inaccessible. A quick test is to tab through the page quickly and ensure you can get focus back to the address bar.