Descriptive. Under the descriptive system of markup, authors identify the element types of text tokens. In Figure 1 the tag
Authors who are accustomed to procedural markup often think of descriptive markup as if it were procedural and may even use tags procedurally. The primary difference is that procedural markup indicates what a particular text formatter should do; descriptive markup indicates what a text element is or, in different terms, declares that a portion of a text stream is a member of a particular class. When a text formatter generates the presentational copy of a descriptively marked-up document, it first reads in a set of rules, written in a procedural markup system, that establish what it should do for each occurrence of each element type. By adjusting this set of rules, the author (or support person) establishes a presentational markup design that will be executed automatically and consistently. Moreover, should there be reason to modify the design, only the rules will require editing: the document files remain intact. Not only will the author be relieved of painful and monotonous hours of mechanical editing, the text will not be exposed to corruption.
Descriptive markup shows the logical structure of the document. A document is viewed as a structure of various types of elements: a book is organized into chapters that contain paragraphs and figures; a magazine is organized into articles that contain paragraphs and photographs, and so on. The user describes what is to be processed rather than how it is to be processed (Coombs et al., 1987). The user of a descriptive markup system need only identify each significant element of the document (such as heading, paragraph, highlighted phrase), assign a mnemonic name (generic identifier) to it, and mark the element in the document using this name. The resulting document will contain information about the component elements and their structural relation.