An instance, which contains the data and markup of the document. HTML refers to the document type as well as the markup language for representing instances of that document type. In HTML documents, tags define the start and end of headings, paragraphs, lists, character highlighting and links. Most HTML elements are identified in a document as a start tag, which gives the element name and attributes, followed by the content, followed by the end tag. This is a paragraph.
Some elements appear as just a start tag.
The content of an element is a sequence of characters and nested elements. Some elements, such as anchors, cannot be nested. Anchors and character highlighting may be put inside other constructs. The content model for a tag defines the syntax permitted for the content. Until support for these idioms is widely deployed, their use is strongly discouraged.