* the relationship type must be http://schemas.openxmlformats.org/officeDocument/2006/relationships/commentAuthors
*/
XSLFCommentAuthors(PackagePart part, PackageRelationship rel) throws IOException, XmlException {
super(part, rel);
CmAuthorLstDocument doc =
CmAuthorLstDocument.Factory.parse(getPackagePart().getInputStream());
_authors = doc.getCmAuthorLst();
}