XML elements in a response

I've seen in this document : http://www.ietf.org/rfc/rfc2518.txt some exemples of DAV request and responses.
But there are still some things I'm not sure about...

When you see that :

<?xml version="1.0" encoding="utf-8" ?>
   <multistatus xmlns="DAV:">
     <response>
         <href>http://www.foo.bar/container/</href>
          <propstat>
               <prop xmlns:R="http://www.foo.bar/boxschema/">
                    <R:bigbox/>
                    <R:author/>
                    <creationdate/>
                    <displayname/>
                    <resourcetype/>
                    <supportedlock/>
               </prop>
              <status>HTTP/1.1 200 OK</status>
          </propstat>
    </response>

What does "multistatus" mean ?
The line xmlns="DAV:" means that DAV is the default namespace ?
And since xmlns:R=... defines the URL of the resource, is R:bigbox a live property ?

Thanx in advance