The large amount of Web content that currently needs to be designed, authored, and maintained has made the need for document-engineering technology clear to Web developers. Terms such as structured document, style sheet, and document transformation were once considered technical jargon used only by SGML zealots. After the success of HTML (W3C, 2000), CSS (Bos, Lie, Lilley, & Jacobs, 1998), XML (Bray, Paoli, & Sperberg-McQueen, 1998), XSLT (Clark, 1999), and related specifications, however, they have become fundamental and well-known ingredients of everyday Web design.