code: public BaseTemplate xmlDeclaration() throws IOException {
          out.write("<?xml ");
          writeAttribute("version", "1.0");
          if (configuration.getDeclarationEncoding() != null) {
              writeAttribute(" encoding", configuration.getDeclarationEncoding());
          }
          out.write("?>");
          out.write(configuration.getNewLineString());
          return this;
      }
docs: Renders an XML declaration header. If the declaration encoding is set in the
  {@link TemplateConfiguration#getDeclarationEncoding() template configuration},
  then the encoding is rendered into the declaration.
  @return this template instance
  @throws IOException