Output.xml

<?xml version="1.0"?>
<test>"'&amp;&lt;&gt;</test>
Now monkey patching
<?xml version="1.0"?>
<test>"'&amp;&lt;&gt;</test>

<!--  Notice there is no XML entity substitution for the single- and double-quotes -->

Source.rb

require 'rubygems'
require 'nokogiri'

# I want to have Nokogiri make the XML entity substitutions for all the characters "'&<>
#
puts Nokogiri::XML::Builder.new { |xml| xml.test %q("'&<>) }.to_xml

puts "Now monkey patching"

class Nokogiri::XML::Node
  alias old_encode_special_chars encode_special_chars
  def encode_special_chars(string)
    old_encode_special_chars(string).gsub("'", "&apos;").gsub('"', "&quot;")
  end
end

puts Nokogiri::XML::Builder.new { |xml| xml.test %q("'&<>) }.to_xml