XMLDecl should be excluded
# Expected
Nokogiri::XML.parse('<?xml version="1.0"?><root></root>').xpath("descendant::node()")
# => [#<Nokogiri::XML::Element:0xb38 name="root">]
# Actual
REXML::XPath.match REXML::Document.new('<?xml version="1.0"?><root></root>'), "descendant::node()"
# => [<?xml ... ?>, <root/>]
REXML::VERSION
# => "3.4.4"
XMLDecl should be excluded