Generalized data markup has four objectives: structure, content, context, and format. Markup can articulate and even dictate structure. Structure in a text object include such concepts as document beginning and end, that the document must have a chapter and at least one or more subchapters and the subchapter(s) must follow the chapter, and so on. Your goal with structure is to render the hierarchical and organizational design of the data and the parts thereof.
Content markup identifies what the data means for example, “This text string represents the title of a sidebar and not the title of the article.” Author, title, date, and telephone number used as tags identify the content characteristics of data.
Context markup labels content so that additional meaning can be derived from a content markup tag such as “title.” A “document type” label or tag would add significant information about the title. In our example about Major League Baseball, a context sensitive tag, “document type,” identifying “title” as coming from a newspaper, would have different connotations from document type equals a legal journal.
Format markup allows you to determine how the document instance will be displayed. Generalized markup designers are moving to portable display markup. A portable display markup uses a style sheet that accompanies the document instance. This makes it much easier to change how a document is displayed. A document instance can have any number of style sheets. Markup indicating the title should be displayed using Times New Roman font, 44 point, bold, and centered at the top of page one could be embedded in the document instance at the point in the document where the title begins. By placing these instructions in a style sheet the document instance is freed from the burden of carrying format information. Style changes become easier.