A specialization of computer language. Each instance of markup language is designed to be used to state facts about the textual content of documents, i.e., the manner in which the text should be presented or its semantic significance. A markup language might be used to communicate textual presentation style, e.g. boldfacing and font size, as is the case with HTML (HTML) or it could be used to tag semantic content (see XML). Also, it is useful to note that often markup languages like XML are not languages in any natural language or formalist sense of the term language . Rather they simply tend to consist of conventions for defining markup of a further language. Note that the markup language for a particular document type might be specified by a markup language that is based on a more general markup language. For instance, there is a very general markup language called SGML that is the basis for other markup languages including HTML and XML.