XSLT itself is actually part of a larger specification, Extensible Stylesheet Language, or XSL. XSL is all about specifying the exact format, down to the millimeter, of documents. The formatting part of XSL, which is a far larger specification than XSLT is based on special formatting objects, and this part of XSL is often called XSL-FO (or XSL:FO, or XSLFO). XSL-FO is an involved topic, because styling your documents with formatting objects can be an intricate process. In fact, XSLT was originally added to XSL to make it easier to transform XML documents into documents that are based on XSL-FO formatting objects.
This book is all about XSLT, but it also provides an introduction to XSL-FO, including how to use XSLT to transform documents to XSL-FO form; after all, XSLT was first introduced to make working with XSL-FO easier. To get started, this chapter examines both XSLT and XSL-FO in overview.