diff --git a/groupdav.php b/groupdav.php
index fb76f619c8..2d123f4c0d 100644
--- a/groupdav.php
+++ b/groupdav.php
@@ -44,4 +44,4 @@ $headertime = microtime(true);
 
 $groupdav = new groupdav();
 $groupdav->ServeRequest();
-//error_log(sprintf("GroupDAV %s request took %5.3f s (header include took %5.3f s)",$_SERVER['REQUEST_METHOD'],microtime(true)-$starttime,$headertime-$starttime));
+error_log(sprintf('GroupDAV %s request: status "%s", took %5.3f s'.($headertime?' (header include took %5.3f s)':''),$_SERVER['REQUEST_METHOD'].($_SERVER['REQUEST_METHOD']=='REPORT'?' '.$groupdav->propfind_options['root']['name']:'').' '.$_SERVER['PATH_INFO'],$groupdav->_http_status,microtime(true)-$starttime,$headertime-$starttime));
diff --git a/phpgwapi/inc/class.groupdav.inc.php b/phpgwapi/inc/class.groupdav.inc.php
index 6cc3858edd..93abe779fb 100644
--- a/phpgwapi/inc/class.groupdav.inc.php
+++ b/phpgwapi/inc/class.groupdav.inc.php
@@ -277,32 +277,40 @@ class groupdav extends HTTP_WebDAV_Server
 	 */
 	function OPTIONS($path, &$dav, &$allow)
 	{
-		list(,$app) = explode('/',$path);
-		switch($app)
+		if (preg_match('#/(calendar|inbox|outbox)/#', $path))
 		{
-			case 'calendar':
-				if (!in_array(2,$dav)) $dav[] = 2;
-				$dav[] = 'access-control';
-				$dav[] = 'calendar-access';
-				$dav[] = 'calendar-auto-schedule';
-				$dav[] = 'calendar-proxy';
-				//$dav[] = 'calendar-availibility';
-				//$dav[] = 'calendarserver-private-events';
-				break;
-			case 'addressbook':
-				if (!in_array(2,$dav)) $dav[] = 2;
-				//$dav[] = 3;	// revision aka versioning support not implemented
-				$dav[] = 'access-control';
-				$dav[] = 'addressbook';	// CardDAV uses "addressbook" NOT "addressbook-access"
-				break;
-			default:	// used eg. for root, and needs all above settings, as some clients only use these!
-				if (!in_array(2,$dav)) $dav[] = 2;
-				$dav[] = 'access-control';
-				$dav[] = 'calendar-access';
-				$dav[] = 'calendar-auto-schedule';
-				$dav[] = 'calendar-proxy';
-				$dav[] = 'addressbook';
+			$app = 'calendar';
 		}
+		elseif (strpos($path, '/addressbook/') !== false)
+		{
+			$app = 'addressbook';
+		}
+		// CalDAV and CardDAV
+		if (!in_array(2,$dav)) $dav[] = 2;
+		$dav[] = 'access-control';
+
+		if ($app !== 'addressbook')	// CalDAV
+		{
+			$dav[] = 'calendar-access';
+			$dav[] = 'calendar-auto-schedule';
+			$dav[] = 'calendar-proxy';
+			// required by iOS iCal to use principal-property-search to autocomplete participants (and locations)
+			$dav[] = 'calendarserver-principal-property-search';
+			// other capabilities calendarserver announces
+			//$dav[] = 'calendar-schedule';
+			//$dav[] = 'calendar-availability';
+			//$dav[] = 'inbox-availability';
+			//$dav[] = 'calendarserver-private-events';
+			//$dav[] = 'calendarserver-private-comments';
+			//$dav[] = 'calendarserver-sharing';
+			//$dav[] = 'calendarserver-sharing-no-scheduling';
+
+		}
+		elseif ($app !== 'calendar')	// CardDAV
+		{
+			$dav[] = 'addressbook';	// CardDAV uses "addressbook" NOT "addressbook-access"
+		}
+		//error_log(__METHOD__."('$path') --> app='$app' --> DAV: ".implode(', ', $dav));
 	}
 
 	/**
@@ -502,7 +510,7 @@ class groupdav extends HTTP_WebDAV_Server
 		$ret = false;
 		foreach($this->propfind_options['props'] as $prop)
 		{
-			if ($prop['name'] == $name && (is_null($ns) || $prop['ns'] == $ns))
+			if ($prop['name'] == $name && (is_null($ns) || $prop['xmlns'] == $ns))
 			{
 				$ret = true;
 				break;
@@ -858,6 +866,11 @@ class groupdav extends HTTP_WebDAV_Server
 		}
 		echo "</table>\n";
 
+		$dav = array(1);
+		$allow = false;
+		$this->OPTIONS($options['path'], $dav, $allow);
+		echo "<p>DAV: ".implode(', ', $dav)."</p>\n";
+
 		echo "</body>\n</html>\n";
 
 		common::egw_exit();
diff --git a/phpgwapi/inc/class.groupdav_principals.inc.php b/phpgwapi/inc/class.groupdav_principals.inc.php
index d171946c75..ffeb2bd303 100644
--- a/phpgwapi/inc/class.groupdav_principals.inc.php
+++ b/phpgwapi/inc/class.groupdav_principals.inc.php
@@ -49,6 +49,9 @@ class groupdav_principals extends groupdav_handler
 		'principal-property-search' => array(
 			'method' => 'principal_property_search_report',
 		),
+		'principal-search-property-set' => array(
+			'method' => 'principal_search_property_set_report',
+		),
 		/*'expand-property' => array(
 			// an other report calendarserver announces
 		),*/
@@ -189,6 +192,43 @@ class groupdav_principals extends groupdav_handler
 	 * but interprets returning all principals (all have a matching calendar-home-set) as NOT supporting CalDAV scheduling
 	 * --> search only current user's principal, when Lightning searches for calendar-home-set
 	 *
+	 * Example from iOS iCal autocompleting invitees using calendarserver-principal-property-search WebDAV extension
+	 * <x0:principal-property-search xmlns:x2="urn:ietf:params:xml:ns:caldav" xmlns:x1="http://calendarserver.org/ns/" xmlns:x0="DAV:" test="anyof">
+	 *   <x0:property-search>
+	 *     <x0:prop>
+	 *       <x0:displayname/>
+	 *     </x0:prop>
+	 *     <x0:match match-type="contains">beck</x0:match>
+	 *   </x0:property-search>
+	 *   <x0:property-search>
+	 *     <x0:prop>
+	 *       <x1:email-address-set/>
+	 *     </x0:prop>
+	 *     <x0:match match-type="starts-with">beck</x0:match>
+	 *   </x0:property-search>
+	 *   <x0:property-search>
+	 *     <x0:prop>
+	 *       <x1:first-name/>
+	 *     </x0:prop>
+	 *     <x0:match match-type="starts-with">beck</x0:match>
+	 *   </x0:property-search>
+	 *   <x0:property-search>
+	 *     <x0:prop>
+	 *       <x1:last-name/>
+	 *     </x0:prop>
+	 *     <x0:match match-type="starts-with">beck</x0:match>
+	 *   </x0:property-search>
+	 *   <x0:prop>
+	 *     <x1:first-name/>
+	 *     <x1:last-name/>
+	 *     <x0:displayname/>
+	 *     <x1:email-address-set/>
+	 *     <x2:calendar-user-address-set/>
+	 *     <x1:record-type/>
+	 *     <x0:principal-URL/>
+	 *   </x0:prop>
+	 * </x0:principal-property-search>
+	 *
 	 * @param string $path
 	 * @param array $options
 	 * @param array &$files
@@ -223,7 +263,7 @@ class groupdav_principals extends groupdav_handler
 					if (isset($property_search) && is_array($search_props[$property_search]))
 					{
 						$search_props[$property_search]['match'] = $prop['data'];
-						// optional match-type: "contains" (default), "starts-with"
+						// optional match-type: "contains" (default), "starts-with", "ends-with", "equals"
 						$search_props[$property_search]['match-type'] = $prop['attrs']['match-type'];
 					}
 					break;
@@ -314,7 +354,7 @@ class groupdav_principals extends groupdav_handler
 	 *
 	 * @param string $value value to test
 	 * @param string $match criteria/sub-string
-	 * @param string $match_type='contains' or 'starts-with'
+	 * @param string $match_type='contains' 'starts-with', 'ends-with' or 'equals'
 	 */
 	private static function match($value, $match, $match_type='contains')
 	{
@@ -335,6 +375,109 @@ class groupdav_principals extends groupdav_handler
 		}
 	}
 
+	/**
+	 * Handle principal-search-property-set report
+	 *
+	 * REPORT /principals/ HTTP/1.1
+	 * <?xml version="1.0" encoding="utf-8" ?>
+	 * <x0:principal-search-property-set xmlns:x0="DAV:"/>
+	 *
+	 * <?xml version='1.0' encoding='UTF-8'?>
+	 * <principal-search-property-set xmlns='DAV:'>
+	 *   <principal-search-property>
+	 *     <prop>
+	 *       <displayname/>
+	 *     </prop>
+	 *     <description xml:lang='en'>Display Name</description>
+	 *   </principal-search-property>
+	 *   <principal-search-property>
+	 *     <prop>
+	 *       <email-address-set xmlns='http://calendarserver.org/ns/'/>
+	 *     </prop>
+	 *     <description xml:lang='en'>Email Addresses</description>
+	 *   </principal-search-property>
+	 *   <principal-search-property>
+	 *     <prop>
+	 *       <last-name xmlns='http://calendarserver.org/ns/'/>
+	 *     </prop>
+	 *     <description xml:lang='en'>Last Name</description>
+	 *   </principal-search-property>
+	 *   <principal-search-property>
+	 *     <prop>
+	 *       <calendar-user-type xmlns='urn:ietf:params:xml:ns:caldav'/>
+	 *     </prop>
+	 *     <description xml:lang='en'>Calendar User Type</description>
+	 *   </principal-search-property>
+	 *   <principal-search-property>
+	 *     <prop>
+	 *       <first-name xmlns='http://calendarserver.org/ns/'/>
+	 *     </prop>
+	 *     <description xml:lang='en'>First Name</description>
+	 *   </principal-search-property>
+	 *   <principal-search-property>
+	 *     <prop>
+	 *       <calendar-user-address-set xmlns='urn:ietf:params:xml:ns:caldav'/>
+	 *     </prop>
+	 *     <description xml:lang='en'>Calendar User Address Set</description>
+	 *   </principal-search-property>
+	 * </principal-search-property-set>
+	 *
+	 * @param string $path
+	 * @param array $options
+	 * @param array &$files
+	 * @param int $user account_id
+	 * @return mixed boolean true on success, false on failure or string with http status (eg. '404 Not Found')
+	 */
+	function principal_search_property_set_report($path,&$options,&$files,$user)
+	{
+		static $search_props = array(
+			// from iOS iCal
+			'displayname' => 'Display Name',
+			'email-address-set' => array('description' => 'Email Addresses', 'ns' => groupdav::CALENDARSERVER),
+			'last-name' => array('description' => 'Last Name', 'ns' => groupdav::CALENDARSERVER),
+			'calendar-user-type' => array('description' => 'Calendar User Type', 'ns' => groupdav::CALENDARSERVER),
+			'first-name' => array('description' => 'First Name', 'ns' => groupdav::CALENDARSERVER),
+			'calendar-user-address-set' => array('description' => 'Calendar User Address Set', 'ns' => groupdav::CALENDARSERVER),
+			// Lightning
+			'calendar-home-set' => array('description' => 'Calendar Home Set', 'ns' => groupdav::CALENDARSERVER),
+			// others, we generally support all properties of the principal
+		);
+		header('Content-type: text/xml; charset=UTF-8');
+
+		$xml = new XMLWriter;
+		$xml->openMemory();
+		$xml->setIndent(true);
+		$xml->startDocument('1.0', 'UTF-8');
+		$xml->startElementNs(null, 'principal-search-property-set', 'DAV:');
+
+		foreach($search_props as $name => $data)
+		{
+			$xml->startElement('principal-search-property');
+			$xml->startElement('prop');
+			if (is_array($data) && !empty($data['ns']))
+			{
+				$xml->writeElementNs(null, $name, $data['ns']);
+			}
+			else
+			{
+				$xml->writeElement($name);
+			}
+			$xml->endElement();	// prop
+
+			$xml->startElement('description');
+			$xml->writeAttribute('xml:lang', 'en');
+			$xml->text(is_array($data) ? $data['description'] : $data);
+			$xml->endElement();	// description
+
+			$xml->endElement();	// principal-search-property
+		}
+		$xml->endElement();	// principal-search-property-set
+		$xml->endDocument();
+		echo $xml->outputMemory();
+
+		common::egw_exit();
+	}
+
 	/**
 	 * Do propfind in /pricipals/users
 	 *