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)
  return :oga if defined?(::Oga)
  REQUIREMENT_MAP.each do |library, parser|
    require library
    return parser
  rescue LoadError
    next
  end
  raise(NoParserError,
    "No XML parser detected. If you're using Rubinius and Bundler, try adding an XML parser to your Gemfile (e.g. libxml-ruby, nokogiri, or rubysl-rexml). For more information, see https://github.com/sferik/multi_xml/issues/42.")
end