system -> String | nil[permalink][rdoc][edit]-
DTD のシステム識別子を返します。
DTD が外部サブセットを含んでいない場合は nil を返します。
require 'rexml/document' doctype = REXML::Document.new(<<EOS).doctype <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> EOS doctype.system # => "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd" doctype.public # => "-//W3C//DTD XHTML 1.0 Strict//EN" doctype = REXML::Document.new(<<EOS).doctype <!DOCTYPE root SYSTEM "foobar"> EOS doctype.system # => "foobar" doctype.public # => nil