# File lib/mechanize/file_response.rb, line 32
  def [](key)
    return nil unless key.downcase == 'content-type'
    return 'text/html' if directory?
    return 'text/html' if ['.html', '.xhtml'].any? { |extn|
      @file_path =~ /#{extn}$/
    }
    nil
  end