As mentioned briefly by Pierre-Alain Joye, the documentation (on the Livedocs website) has been updated for the XMLWriter package.

This is the XMLWriter extension. It wraps the libxml xmlWriter API.

This extension represents a writer that provides a non-cached, forward-only means of generating streams or files containing XML data. This extension can be used in an object oriented style or a procedural one. Every method documented describes the alternative procedural call.

The updated documentation cn be found here.