You use XSLT to manipulate documents, changing and working with their markup as you want. One of the most common transformations is from XML documents to HTML documents, and that's the kind of transformation we'll see in the examples in this chapter.
To create an XSLT transformation, you need two documents—the document to transform, and the style sheet that specifies the transformation. Both documents are well-formed XML documents.
Here's an example; this document, planets.xml, is a well-formed XML document that holds data about three planets—Mercury, Venus, and Earth. Throughout this chapter, I'll transform this document to HTML in various ways. For programs that can understand it, you can use the