.
  def each_capitalized
    block_given? or return enum_for(__method__) { @header.size }
    @header.each do |k,v|
      yield capitalize(k), v.join(', ')
    end
  end

  alias canonical_each each_capitalized

  def capitalize(name)
    name.to_s.split(/-/).map {|s| s.capitalize }.join('-')
  end
  private :capitalize

  # Returns an array of Range objects that represent
  # the value of field <tt>'Range'</tt>,
  # or +nil+ if there is no such field;
  # see {Range request header}[https://en.wikipedia.org/wiki/List_of_HTTP_header_fields#range-request-header]:
  #
  #   req = Net::HTTP::Get.new(uri)
  #   req['Range'] = 'bytes=0-99,200-299,400-499'
  #   req.range # => [0..99, 200..299, 400..499]
  #   req.delete('Range')
  #   req.range # # => nil
  #
  def range
    return nil unless @header['range']

    value = self['Range']
    # byte-range-set = *( "," OWS ) ( byte-range-spec / suffix-byte-range-spec )
    #   *( OWS "," [ OWS ( byte-range-spec / suffix-byte-range-spec ) ] )
    # corrected collected ABNF
    # http://tools.ietf.org/html/draft-ietf-httpbis-p5-range-19#section-5.4.1
    # http://tools.ietf.org/html/draft-ietf-httpbis-p5-range-19#appendix-C
    # http://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-19#section-3.2.5
    unless /\Abytes=((?:,[ \t]*)*(?:\d+-\d*|-\d+)(?:[ \t]*,(?:[ \t]*\d+-\d*|-\d+)?)*)\z/ =~ value
      raise Net::HTTPHeaderSyntaxError, "invalid syntax for byte-ranges-specifier: '#{value}'"
    end

    byte_range_set = $1
    result = byte_range_set.split(/,/).map {|spec|
      m = /(\d+)?\s*-\s*(\d+)?/i.match(spec) or
              raise Net::HTTPHeaderSyntaxError, "invalid byte-range-spec: '#{spec}'"
      d1 = m[1].to_i
      d2 = m[2].to_i
      if m[1] and m[2]
        if d1 > d2
          raise Net::HTTPHeaderSyntaxError, "last-byte-pos MUST greater than or equal to first-byte-pos but '#{spec}'"
        end
        d1..d2
      elsif m[1]
        d1..-1
      elsif m[2]
        -d2..-1
      else
        raise Net::HTTPHeaderSyntaxError, 'range is not specified'
      end
    }
    # if result.empty?
    # byte-range-set must include at least one byte-range-spec or suffix-byte-range-spec
    # but above regexp already denies it.
    if result.size == 1 && result[0].begin == 0 && result[0].end == -1
      raise Net::HTTPHeaderSyntaxError, 'only one suffix-byte-range-spec with zero suffix-length'
    end
    result
  end

  # call-seq:
  