Triggering of Events by Mouse Pointer Location
You should avoid having events triggered by movements of the mouse pointer over or off a special area. If you must include triggering, you should make it optional.
Some accessibility aids require the mouse pointer to move when information is explored on the screen. For example, a screen review utility may move the mouse to follow words being read, or a user may need to move the mouse to enlarge certain text.
Reliance on a mouse pointer can be a problem if movement of the mouse causes unexpected results. For example, if text appears when the mouse moves over an object and disappears when the mouse moves off of it, the text essentially disappears each time the user tries to read it!
There are two cases where it is acceptable to trigger changes based on mouse pointer movement, because these cases are already understood by accessibility aids and handled appropriately:
- It is acceptable to change the shape of the mouse pointer as it is moved. For example, you can change the shape to indicate whether or not an object is a valid drop target.
- It is acceptable, and in fact encouraged, to use tooltip controls to display an object's name or other explanatory information when the pointer is paused over an object. However, this is only the case if a standard tooltip control is used rather than a custom implementation.