The intent of this Success Criterion is to ensure that functionality is predictable as visitors navigate their way through a document. Any component that is able to trigger an event when it receives focus must not change the context. Examples of changing context when a component receives focus include, but are not limited to:
Focus may be moved to a control either via the keyboard (e.g. tabbing to a control) or the mouse (e.g. clicking on a text field). Moving the mouse over a control does not move the focus unless scripting implements this behavior. Note that for some types of controls, clicking on a control may also activate the control (e.g. button), which may, in turn, initiate a change in context.
What is meant by "component" here is also sometimes called "user interface element" or "user interface component''.
Example 1: A dropdown menu
A dropdown menu on a page allows users to choose between jump destinations. If the person uses the keyboard to move down to a choice and activates it (with a spacebar or enter key) it will jump to a new page. However, if the person moves down to a choice and either hits the escape or the tab key to move out of the pulldown menu – it does not jump to a new screen as the focus shifts out of the dropdown menu.
Example of a Failure: A help dialog
When a field receives focus, a help dialog window describing the field and providing options opens. As a keyboard user tabs through the Web page, the dialog opens, moving the keyboard focus away from the control every time the user attempts to tab past the field.
A change of content is not always a change of context. This success criterion is automatically met if changes in content are not also changes of context.