This chapter sends you off by bringing this book's topics full circle. We return to many of the themes about XML processing in Perl that we introduced in Chapter 3, but in the context of all the detailed material that we've covered in the interceding chapters. Our intent is to take you on one concluding tour through the world of Perl and XML, with its strategies and its gotchas, before sending you on your way.
You've seen XML namespaces used since we first mentioned this concept back in Chapter 2. Many XML applications, such as XSLT, insist that all their elements claim fealty to a certain namespace. The deciding factor here usually involves how symbiotic the application is in its usual use: does it usually work on its own, with a one-document-per-application style, or does it tend to mix with other sorts of XML?
DocBook XML, for example, is not very symbiotic. An instance of DocBook is almost always a whole XML document, defining a book or an article, and all the elements within such a document that aren't explicitly tied to some other namespace are found in the official DocBook documentation. However, within a DocBook document, you might encounter a clump of MathML elements making their home in a rather parasitic fashion, nestled in among the folds of the DocBook elements, from which it derives nourishing context.
This sort of thing is useful for two reasons: first, DocBook, while its element spread tries to cover all kinds ...