TIP 83

Don't design solely for mouse users

Not everyone can use a mouse. If you can't see, you can't see where the mouse cursor is positioned on the page. If you have impaired mobility, you may not be able to hold the mouse, or manage the fine degree of control required for some mouse movements.

Don't require users to be able to click on a small or moving target in order to proceed to another page. Offer additional plain text links.

Give some thought to the TAB order of the various links and form elements on the page. The default is the order in which these elements appear in the HTML code. In most cases, this is appropriate, but in some instances, it may make more sense for a different TAB order to be set up - you can do this using the TABINDEX attribute.

Make sure event handlers do not require use of a mouse

For event handlers that do more than just change the presentation of an element, such as change color when the mouse moves over an item, consider the following:

Use application-level event triggers rather than user interaction-level triggers. In HTML 4.0, application-level event attributes are "onfocus", "onblur" (the opposite of "onfocus"), and "onselect". These events are triggered when something happens on the page regardless of how the user causes it to happen. For example, an "onfocus" event occurs when a control receives the focus, whether that is done by clicking the mouse or by using the keyboard. By contrast, device-dependent events only occur when a particular device is in use. A "onmousedown" event, which also can give a control the focus, is only triggered by a mouse action, and other means of giving focus to the control will not be responded to

If you must use device-dependent attributes, provide redundant input mechanisms; for example, specify two handlers for the same element, both of which have the same code associated with them:

Device Handler Correspondences

Rationale

Event handlers respond to user actions, such as mouse movement, typing, voice input, etc. On web pages, event handlers often just change the presentation of an element, such as by changing the color of an image. Others, however, are parts of the functionality of the page. This functionality needs to be presented in a device-independent way so all users can access it, since not all users use a mouse.

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