code: public String getDocumentTypeDeclarationPublicIdentifier()
    {
  
      Document doc;
  
      if (m_root.getNodeType() == Node.DOCUMENT_NODE)
        doc = (Document) m_root;
      else
        doc = m_root.getOwnerDocument();
  
      if (null != doc)
      {
        DocumentType dtd = doc.getDoctype();
  
        if (null != dtd)
        {
          return dtd.getPublicId();
        }
      }
  
      return null;
    }
docs: Return the public identifier of the external subset,
  normalized as described in 4.2.2 External Entities [XML]. If there is
  no external subset or if it has no public identifier, this property
  has no value.
  
  @return the public identifier String object, or null if there is none.