XSL rules like these are contained in an XSL Stylesheet, which is just a plain text file filled with formatting instructions that look like the following example. <fo:page-sequence master-name=”easy”> <fo:flow flow-name=”xsl-region-body”> <fo:block font-family=”Serif”>Serif font</fo:block> </fo:flow> </fo:page-sequence> Note that this XSL is written in something that resembles XML. That is more than mere coincidence because, ironically, XSL is actually written in XML and is itself an XML vocabulary. If your head is spinning around, hang on. XSL is used to format XML, which in turn is used as the language for defining XSL. The circular logic can be confus- ing, but fortunately, you don’t need to worry about the particulars of how that all works — just know that it does. Actually, the fact that XSL uses XML to describe its instructions makes it far easier to learn than trying to grasp yet another language syntax. When XSL was conceived by the W3C, the original intention of XSL was simply to provide a way to format XML data. However, after people began to use XML in the real world, it was discovered that something more was needed besides assigning font colors and margin indentions to the content. True, developers needed to be able to style XML in a way that was easily readable, but they also discovered a need to change an XML document from one XML structure to another, as well as to have the ability to easily convert XML Document XSL Processor XSL Stylesheet XSL Output Figure 1-2: Using XSL to apply formatting to XML documents. 13 Chapter 1: Introducing the X-Team