The previous example was illegal because it contained two elements
   that were explicitly banned from appearing together in the propfind
   element.  However, XML is an extensible language, so one can imagine
   new elements being defined for use with propfind.  Below is the
   request body of a PROPFIND and, like the previous example, must be
   rejected with a 400 (Bad Request) by a server that does not
   understand the expired-props element.

   <?xml version="1.0" encoding="utf-8" ?>
   <D:propfind xmlns:D="DAV:"
   xmlns:E="http://www.foo.bar/standards/props/">
     <E:expired-props/>
   </D:propfind>

   To understand why a 400 (Bad Request) is returned let us look at the
   request body as the server unfamiliar with expired-props sees it.

   <?xml version="1.0" encoding="utf-8" ?>
   <D:propfind xmlns:D="DAV:"
               xmlns:E="http://www.foo.bar/standards/props/">
   </D:propfind>

   As the server does not understand the expired-props element,
   according to the WebDAV-specific XML processing rules specified in
   section 14, it must ignore it.  Thus the server sees an empty
   propfind, which by the definition of the propfind element is illegal.

   Please note that had the extension been additive it would not
   necessarily have resulted in a 400 (Bad Request).  For example,
   imagine the following request body for a PROPFIND:

   <?xml version="1.0" encoding="utf-8" ?>
   <D:propfind xmlns:D="DAV:"
               xmlns:E="http://www.foo.bar/standards/props/">




 
RFC 2518                         WEBDAV                    February 1999


     <D:propname/>
     <E:leave-out>*boss*</E:leave-out>
   </D:propfind>

   The previous example contains the fictitious element leave-out. Its
   purpose is to prevent the return of any property whose name matches
   the submitted pattern.  If the previous example were submitted to a
   server unfamiliar with leave-out, the only result would be that the
   leave-out element would be ignored and a propname would be executed.











































 
RFC 2518                         WEBDAV                    February 1999


23.4 Appendix 4 -- XML Namespaces for WebDAV