/**
  * This method is used to search for principals matching a set of
  * properties.
  *
  * This search is specifically used by RFC3744's principal-property-search
  * REPORT. You should at least allow searching on
  * http://sabredav.org/ns}email-address.
  *
  * The actual search should be a unicode-non-case-sensitive search. The
  * keys in searchProperties are the WebDAV property names, while the values
  * are the property values to search on.
  *
  * If multiple properties are being searched on, the search should be
  * AND'ed.
  *
  * This method should simply return a list of 'child names', which may be
  * used to call $this->getChild in the future.
  *
  * @param array $searchProperties
  * @return array
  */
 public function searchPrincipals(array $searchProperties)
 {
     $result = $this->principalBackend->searchPrincipals($this->principalPrefix, $searchProperties);
     $r = array();
     foreach ($result as $row) {
         list(, $r[]) = DAV\URLUtil::splitPath($row);
     }
     return $r;
 }