HTML or HyperText Markup Language is a markup language for content on the web. In an HTML document, various HTML tags surround content and denote certain types of HTML elements, such as paragraphs or headings. Web pages marked up with HTML are served by a web server and displayed in users' web browsers.

XHTML is considered by the W3C to be HTML's successor. Web Services attempts to have every site they maintain validate as XHTML 1.0 transitional.