A markup language is a system for noting the attributes of a document. Historically, the term "markup" has been used to refer to the process of marking manuscript copy for typesetting, usually with directions for the use of type fonts and sizes, spacing, indentation, and other formatting features. In the electronic era, "markup" refers to the sequence of characters or other symbols that are inserted within a text or word processing file to describe the document's logical structure or indicate how the document should appear when it is displayed or printed. (Notation entered with the intention of describing logical properties is usually referred to as descriptive markup, whereas notation concerned with formatting is referred to as procedural markup.)

Unlike programming languages, which are dynamic and process data through various calculations, markup languages are static. In essence, a markup language identifies similar units of information...