module MultiXml

def default_parser

to see which are installed if none are loaded.
if any parsers are already loaded, then checks
have loaded and installed. First checks to see
The default parser based on what you currently 
def default_parser
  return :ox if defined?(::Ox)
  return :libxml if defined?(::LibXML)
  return :nokogiri if defined?(::Nokogiri)
  REQUIREMENT_MAP.each do |(library, parser)|
    begin
      require library
      return parser
    rescue LoadError
      next
    end
  end
end