class Nokogiri::XML::DTD

def each
  attributes.each do |key, value|
    yield([key, value])
  end
end

def html5_dtd?
  html_dtd? &&
    external_id.nil? &&
    (system_id.nil? || system_id == 'about:legacy-compat')
end

def html_dtd?
  name.casecmp('html').zero?
end

def keys
  attributes.keys
end