PHP's XML extensions, especially those that ship with newer versions of the language, are more than sufficient for most development tasks. However, if your PHP build doesn't support a particular XML extension, and you're not in a position to recompile a new build, your development efforts can get rapidly derailed. Further, many of PHP's built-in extensions are still experimental and in a state of flux. In such a situation, an external class that is more stable (and perhaps also easier to use) is often a viable option.A number of open source XML/PHP projects are available to work around the problem. Implemented as PHP classes that can easily be included in your application, they allow you, the developer, to reproduce the functionality of PHP's native XML functions in environments in which these native functions are not supported.This chapter provided a quick-and-dirty crash course in the basics of each implementation, demonstrating its viability in real-world application development with simple examples and re-creations of applications from previous chapters. Each of these implementations is freely available on the Internet, together with supporting examples and (in most cases) good documentation.If the implementations discussed in this chapter don't meet your requirements, don't despair. The PHP developer community is fairly restless, and it's quite likely that someone, somewhere, has decided to create and release a piece of code that does exactly what you need. Drop by this book's companion web site for a more comprehensive, frequently updated list of available XML/PHP alternatives, and take a look for yourself.The next (and final) chapter of this book takes things a step further, demonstrating how all the theory you've learned thus far can be applied in the real world. Case studies, coming up next.