I think this book is a great idea, but I'll never buy it. I currently use PHP to generate HTML, and I'd like to move to XML, so it's the perfect topic for me. But books go out of date fast, and there's too many free resources on the web that are constantly being updated.

So, does anyone know of any good links for learning about the use of PHP with XML? I know I could google for some (and I have), I was just wondering if anyone has something that they would recommend.