# 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