public static String getDefaultXhtmlNamespace(Project project) {
    final String doctype = ExternalResourceManagerEx.getInstanceEx().getDefaultHtmlDoctype(project);
    return Html5SchemaProvider.getHtml5SchemaLocation().equals(doctype)
           ? Html5SchemaProvider.getXhtml5SchemaLocation()
           : doctype;
  }
public static String getDefaultXhtmlNamespace(Project project)