code: public static Object documentType(DocumentType dtd, String[][] entities, String[][] notations) {
          return new Object[]{
                  dtd.getNodeType(),// short
                  dtd.getName(),// String
                  entities,// NamedNodeMap
                  notations,// NamedNodeMap
                  dtd.getPublicId(),// String
                  dtd.getSystemId(),// String
                  dtd.getInternalSubset() //String
          };
      }
docs: Each Document has a doctype attribute whose value is either null or a DocumentType object.
  The DocumentType interface in the DOM Core provides an interface to the list of entities
  that are defined for the document, and little else because the effect of namespaces and
  the various XML schema efforts on DTD representation are not clearly understood as of
  this writing.
  <p>
  DOM Level 3 doesn't support editing DocumentType nodes. DocumentType nodes are read-only.