The X-Team through HTML Eyes You may be approaching the X-Team after having already worked with HTML. If so, when you look at XML and XSLT, it’s natural to view these new technolo- gies through HTML eyes. Having a knowledge of HTML definitely gives you a head start in learning XML syntax; noting the similarities and differences between them is important. Although I compare HTML and XML in this section, remember that XSL and XSLT stylesheets are both written using XML, so the same rules apply to them as to XML. XML looks a lot like HTML . . . If you can read HTML, you quickly see that XML looks an awful lot like HTML in terms of its syntax. For example, a document title in HTML is defined as <title>My Document Title</title> Like HTML, the element is the primary building block of XML. Therefore, a book title in XML might be defined to look something like this: <book>War and Peace</book> Additionally, XML follows HTML in using name-value pairs inside elements to provide additional descriptive information about an element. <invoice id=”110”> <company>Polar Salsa Corporation</company> </invoice> In this XML snippet, the id attribute provides additional information related to the invoice element. But XML isn’t the same as HTML . . . HTML and XML have a definite likeness, but you should watch out for some significant variations in syntax rules. The three most important are as follows. XML is well-formed HTML has always been lenient in some of its syntax requirements, not always forcing you to have closing tags on some of the elements, such as the para- graph (<p>) element. For example, both of the following lines are valid HTML: 17 Chapter 1: Introducing the X-Team