PHP で SimpleXML を使用してハイフネーションされた XML ノード名にアクセスする方法

<gnm:Workbook xmlns:gnm="http://www.gnumeric.org/v10.dtd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.gnumeric.org/v9.xsd">
  <office:document-meta xmlns:office="urn:oasis:names:tc:opendocument:xmlns:office:1.0" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:meta="urn:oasis:names:tc:opendocument:xmlns:meta:1.0" office:version="1.1">
    <office:meta>
      <dc:creator>Mark Baker</dc:creator>
      <dc:date>2010-09-01T22:49:33Z</dc:date>
      <meta:creation-date>2010-09-01T22:48:39Z</meta:creation-date>
      <meta:editing-cycles>4</meta:editing-cycles>
      <meta:editing-duration>PT00H04M20S</meta:editing-duration>
      <meta:generator>OpenOffice.org/3.1$Win32 OpenOffice.org_project/310m11$Build-9399</meta:generator>
    </office:meta>
  </office:document-meta>
</gnm:Workbook>

$xml = simplexml_load_string($gFileData);
$namespacesMeta = $xml->getNamespaces(true);
$officeXML = $xml->children($namespacesMeta['office']);
var_dump($officeXML);

echo '<hr />';

$docMeta = $officeXML->{'document-meta'};
var_dump($docMeta);