Markup, as you can see from this list, is a word that covers a whole lot of territory; in fact, most of the rest of the spec is little more than a discussion of the different kinds of markup and how they are used.
One of the nice things about XML is markup can easily be distinguished from text because it always begins either with the character < (in which case it ends with the character >) or the character & (in which case it ends with the character ;).
Copyright © 1998, Tim Bray. All rights reserved.