Description:
------------
xmlns:D="DAV:" is actually used throughout the DAV RFC.

On another topic, DOMImplementation->createDocumentType("DAV:",...) segfaults.

Reproduce code:
---------------
<?php

// PROPFIND response (Apache2/DAV2)
$xml = <<<DAVXML
<?xml version="1.0" encoding="utf-8"?>
<D:multistatus xmlns:D="DAV:">
<D:response xmlns:lp1="DAV:" xmlns:lp2="http://apache.org/dav/props/">
<D:href>/</D:href>
<D:propstat>
<D:prop>
<lp1:resourcetype><D:collection/></lp1:resourcetype>
<lp1:creationdate>2005-11-12T11:25:47Z</lp1:creationdate>
<lp1:getlastmodified>Sat, 12 Nov 2005 11:25:47 GMT</lp1:getlastmodified>
<lp1:getetag>"19737a-1000-7fda84c0"</lp1:getetag>
<D:supportedlock>
<D:lockentry>
<D:lockscope><D:exclusive/></D:lockscope>
<D:locktype><D:write/></D:locktype>
</D:lockentry>
<D:lockentry>
<D:lockscope><D:shared/></D:lockscope>
<D:locktype><D:write/></D:locktype>
</D:lockentry>
</D:supportedlock>
<D:lockdiscovery/>
<D:getcontenttype>httpd/unix-directory</D:getcontenttype>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
</D:multistatus>
DAVXML;

$dom = new DOMImplementation;
$dtd = $dom->createDocumentType("webdav", "", 
        "http://dev.iworks.at/webdav-1.0.dtd");
$doc = $dom->createDocument("", "", $dtd);
$doc->validateOnParse = true;
$doc->loadXML($xml);

?>

Expected result:
----------------
Validation success

Actual result:
--------------
Notice: DOMDocument::loadXML(): xmlns:D: 'DAV:' is not a valid URI in Entity, line: 2 in ...

Notice: DOMDocument::loadXML(): Validation failed: no DTD found !xmlns:lp1: 'DAV:' is not a valid URI in Entity, line: 3 in ...