Whenever an author writes anything, he or she “marks it up.” For example, spaces between words indicate word boundaries, commas indicate phrase boundaries, and periods indicate sentence boundaries. This fact is widely ignored: indeed, markup is usually treated as an unfortunate requirement of using electronic text-processing systems, that is, as something to be avoided. A careful analysis, however, reveals that authors regularly use two types of markup in their manuscripts: punctuational, for example, placing periods at ends of sentences; and presentational, for example, numbering pages. Thus, markup cannot be escaped because our writing systems require it.