In an HTML document, HTML elements are tags, as well as text, which act as indicators to a web browser as to how the document is to be interpreted by the browser and ultimately presented on the user's computer screen. HTML is a structured markup language, and the HTML elements are SGML elements that meet the requirements of one or more of the HTML Document Type Definitions (DTDs). These elements have properties: both attributes and content, some of which are either allowable or required, according to the appropriate HTML DTD. If an element is unknown to the web browser, it will be ignored. Elements may represent headings, paragraphs, hypertext links, lists, embedded media, and a variety of other structures.