This technique relates to the following sections of the guidelines:
Giving focus to elements in an order that follows sequences and relationships within the content.
Some Web content must support sequential navigation. For example, a person using a keyboard or keyboard interface to complete an online form typically uses the tab key to move from one input element to the next item on the form. Each time the user presses the tab key, another element receives focus. The user's next action will affect the item that has focus. In some cases it may be necessary to specify the order in which the focus will move from item to item, because the default order is not logical.
A company's Web site includes a form that collects marketing data and allows users to subscribe to several newsletters published by the company. The form includes typical fields such as name, street address, city, state or province, and postal code. It also includes several checkboxes so that users can indicate which newsletters they want. An individual using a screen magnifier enters her name and street address and presses the tab key, expecting that she will next enter the name of her city. But instead the focus moves to a checkbox beside the name of a newsletter. Only part of the newsletter's title is visible because of the screen magnification, and the user does not realize what has happened. She keys in her address and submits the form. She is surprised when she receives an error message telling her that one or more required fields is incomplete.
Editorial Note: The title (short-name) of this technique (15.7 in HTML Techniques) is misleading, since the technique also addresses use of tabindex to control tab order for links and objects as well as form controls. We might consider a more informative short-name.