My reason for suggesting this is that i have found the PHP DOM library to be immensely powerful and useful, indeed it forms the backbone of all the CMS's that I have written and a lot of other things too.
BUT - I've discovered that each language's implementation of DOM seems to have its own little quirks and nuances that can have you sat there for ages thinking "WTF??" until you figure out that it's a peculiarity of that particular implementation. PHP's implementation is no exception! E.g. you can run into all sorts of memory pollution problems with the DOMNodeList class, if you're not careful (so I've discovered the hard way!). There are various other subtleties that I've learned the hard way too.
To have a PHP of sub-forum would be very helpful.