Semantic HTML and its role in web accessibility

Semantic HTML is the practice of using HTML elements based on their intended meaning rather than their visual appearance. This approach allows software, including screen readers, search engine crawlers, and AI agents, to interpret the structure and purpose of web content effectively.

Key structural elements include landmark elements like header, nav, main, aside, footer, and search, which divide a page into regions. Other elements such as h1 through h6 for headings, ul and ol for lists, and article or section for thematic grouping help organize content. Specific inline elements, such as time and button, provide additional context for machine-readable data and user actions.

Proper implementation is critical for web accessibility. Under the W3C HTML Accessibility API Mappings (HTML-AAM) specification, these elements are parsed into an accessibility tree that exposes roles and states to assistive technologies. Common accessibility improvements include adding descriptive alt text to images, ensuring form fields have properly associated labels, and maintaining a logical heading hierarchy to assist user navigation.