It escapes the single use trap of procedural markup. Descriptive structural markup identifies document components and their logical relationship. Structural elements are components that you usually want to present visually in some distinct manner. Examples are chapter titles, paragraphs, block quotes, and the like. Descriptive nominal markup, as you might expect, identifies named entities, both concrete and abstract.
Examples are corporate names, personal names, topical subjects, genres, and geographic names.
While you may want to visually present these names online or on paper in some particular manner, you usually want to index them in particular ways, to use them to provide access to the source or subject matter of the document. Referential Markup . As its name suggests, referential markup refers to information that is not present. There are different kinds and ways that one might use referential markup, but I would like to focus on the kind of referential markup that enables something about which most of you have heard, and perhaps with which many of you have some experience, namely, hypertext and hypermedia. It is possible not only to refer to or point at this other digital information from within SGML based documents, but also to control the notation information needed to launch the devices necessary for rendering the various objects into humanly intelligible forms.