Complex components such as tabs, accordions, menus, and carousels require deliberate accessibility design because the browser cannot infer their interactive behavior. An accessible tab interface uses role="tablist", role="tab", and role="tabpanel", supports arrow-key navigation between tabs, and uses aria-selected to mark the active tab. An accessible accordion renders the header as a <button> with aria-expanded reflecting the open state and points aria-controls or aria-labelledby to the content panel. Carousels should announce the current slide, indicate total slide count, support keyboard navigation, and provide a visible pause control because auto-advancing motion can disorient users and conflict with prefers-reduced-motion. Popup menus should use role="menu" and role="menuitem" only when they behave like desktop application menus; typical website navigation should stay as plain landmark navigation.
Modal dialogs deserve particular care because they intercept the user's attention. The accessibility checklist for a modal includes moving focus into the dialog when it opens, trapping focus inside until it closes, supporting Escape to close, restoring focus to the trigger element on close, exposing role="dialog" with aria-modal="true", and pointing aria-labelledby at the dialog's title. The native <dialog> element opened with showModal() handles focus trapping, an inert backdrop, and Escape-to-close automatically, while show() opens the dialog non-modally for cases such as chat widgets where the rest of the page should remain interactive. Non-modal dialogs should still expose their semantics and accept keyboard focus appropriately.
Dynamic content that updates without a full page reload is invisible to screen readers unless it is announced through a live region. aria-live="polite" tells the screen reader to announce updates when it is idle, which is appropriate for non-urgent information such as form validation summaries or success messages. aria-live="assertive" interrupts current speech and is reserved for urgent alerts such as errors that block a workflow, and role="alert" implies both assertive and aria-atomic behavior in a single attribute. The aria-atomic property tells assistive technology whether to announce the entire region when any part changes or only the changed portion. Updates within a live region are announced in DOM order, and very rapid updates can be skipped, so the implementation should be deliberate. Developers can also inspect the browser's accessibility tree in Chrome DevTools under the Elements tab or in Firefox DevTools to verify how their markup is exposed to assistive technologies.