PHP Magazine has a note today concerning a post over on Christian Stocker's weblog about the XMLReader module that will be included in PHP 5.1.

Finally, XMLReader made it into the standard PHP distribution for the upcoming 5.1. No more fiddling with pecl (which works fine, btw ;) ), if you want XMLReader built in. It's not enabled by default, but it's in the sources and doesn't have more dependencies than DOM or SimpleXML (that is libxml2 2.6.x).

Documentation is a little bit sparse right now, but see my slides, my posts about Processing Large XML Documents (plus Update), the xmlreader interface tutorial from xmlsoft.org (this is for the C API, but the PHP API is very close and a good introduction into the general idea of xmlreader) or just look at the sources and search for {{{ proto (generally a good idea, if documentation is missing for an extension).

It definitely sounds like this will be a much welcome advancement in PHP/XML interfacing, helping put a more standard API on top of any XML document - especially larger ones. Also, if you're looking to give this a shot earlier than PHP 5.1, it also works with PHP 5.0, if installed from pecl.