names=stand_alone?
visibility=public
kind=defined

--- stand_alone? -> String
XML 宣言の standalone の値を文字列で返します。

==== 例
  require 'rexml/document'
  doc = REXML::Document.new(<<EOS)
  <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
  <e />
  EOS
  doc.stand_alone? # => "yes"

