WebDAV
WebDAV is an XML based protocol, it defines a set of new methods (PROPFIND, PROPPATCH, MKCOL, COPY, MOVE, LOCK, UNLOCK) and a set of new headers (DAV, Depth, If, Destination, ...). A good overview of WebDAV: WebDAV in 2 minutes
http://www.w3.org/Jigsaw/Doc/User/webdav.html