What is the "Tab index" attribute used for?

The "Tab index" attribute is crucial for improving web accessibility by determining the order in which interactive elements, such as links and form inputs, receive focus when a user navigates a webpage using the keyboard. This is especially important for users who rely on keyboard navigation instead of a mouse.

When the "Tab" key is pressed, the browser moves focus through the elements on the page in the order specified by the tab index values. Elements with a tab index of "0" are navigated in the order they appear in the document, while a positive tab index value allows developers to define a custom focus order. This helps create a more intuitive and accessible experience for users who may have mobility impairments, as it allows them to navigate the page efficiently without needing to use a mouse.

The other options relate to different aspects of web development and functionality that do not pertain to the "Tab index" attribute specifically. For example, setting priorities for search engines is related to search engine optimization, modifying element sizes deals with styling, and managing browser cookies is a function of client-side storage. None of these options address the primary role of the "Tab index" in keyboard navigation and focus management.