# File date/format.rb, line 200
  def strftime(fmt='%F')
    fmt.gsub(/%([-_0^#]+)?(\d+)?[EO]?(:{1,3}z|.)/m) do |m|
      f = {}
      s, w, c = $1, $2, $3
      if s
        s.scan(/./) do |k|
          case k
          when '-'; f[:p] = '-'
          when '_'; f[:p] = "\s"
          when '0'; f[:p] = '0'
          when '^'; f[:u] = true
          when '#'; f[:x] = true
          end
        end
      end
      if w
        f[:w] = w.to_i
      end
      case c
      when 'A'; emit_ad(DAYNAMES[wday], 0, f)
      when 'a'; emit_ad(ABBR_DAYNAMES[wday], 0, f)
      when 'B'; emit_ad(MONTHNAMES[mon], 0, f)
      when 'b'; emit_ad(ABBR_MONTHNAMES[mon], 0, f)
      when 'C'; emit_sn((year / 100).floor, 2, f)
      when 'c'; emit_a(strftime('%a %b %e %H:%M:%S %Y'), 0, f)
      when 'D'; emit_a(strftime('%m/%d/%y'), 0, f)
      when 'd'; emit_n(mday, 2, f)
      when 'e'; emit_a(mday, 2, f)
      when 'F'
        if m == '%F'
          format('%.4d-%02d-%02d', year, mon, mday) # 4p
        else
          emit_a(strftime('%Y-%m-%d'), 0, f)
        end
      when 'G'; emit_sn(cwyear, 4, f)
      when 'g'; emit_n(cwyear % 100, 2, f)
      when 'H'; emit_n(hour, 2, f)
      when 'h'; emit_ad(strftime('%b'), 0, f)
      when 'I'; emit_n((hour % 12).nonzero? || 12, 2, f)
      when 'j'; emit_n(yday, 3, f)
      when 'k'; emit_a(hour, 2, f)
      when 'L'
        emit_n((sec_fraction / (1.to_r/86400/(10**3))).round, 3, f)
      when 'l'; emit_a((hour % 12).nonzero? || 12, 2, f)
      when 'M'; emit_n(min, 2, f)
      when 'm'; emit_n(mon, 2, f)
      when 'N'
        emit_n((sec_fraction / (1.to_r/86400/(10**9))).round, 9, f)
      when 'n'; "\n"
      when 'P'; emit_ad(strftime('%p').downcase, 0, f)
      when 'p'; emit_au(if hour < 12 then 'AM' else 'PM' end, 0, f)
      when 'Q'
        d = ajd - self.class.jd_to_ajd(self.class::UNIXEPOCH, 0)
        s = (d * 86400*10**3).to_i
        emit_sn(s, 1, f)
      when 'R'; emit_a(strftime('%H:%M'), 0, f)
      when 'r'; emit_a(strftime('%I:%M:%S %p'), 0, f)
      when 'S'; emit_n(sec, 2, f)
      when 's'
        d = ajd - self.class.jd_to_ajd(self.class::UNIXEPOCH, 0)
        s = (d * 86400).to_i
        emit_sn(s, 1, f)
      when 'T'
        if m == '%T'
          format('%02d:%02d:%02d', hour, min, sec) # 4p
        else
          emit_a(strftime('%H:%M:%S'), 0, f)
        end
      when 't'; "\t"
      when 'U', 'W'
        emit_n(if c == 'U' then wnum0 else wnum1 end, 2, f)
      when 'u'; emit_n(cwday, 1, f)
      when 'V'; emit_n(cweek, 2, f)
      when 'v'; emit_a(strftime('%e-%b-%Y'), 0, f)
      when 'w'; emit_n(wday, 1, f)
      when 'X'; emit_a(strftime('%H:%M:%S'), 0, f)
      when 'x'; emit_a(strftime('%m/%d/%y'), 0, f)
      when 'Y'; emit_sn(year, 4, f)
      when 'y'; emit_n(year % 100, 2, f)
      when 'Z'; emit_au(strftime('%:z'), 0, f)
      when /\A(:{0,3})z/
        t = $1.size
        sign = if offset < 0 then -1 else +1 end
        fr = offset.abs
        hh, fr = fr.divmod(1.to_r/24)
        mm, fr = fr.divmod(1.to_r/1440)
        ss, fr = fr.divmod(1.to_r/86400)
        if t == 3
          if    ss.nonzero? then t =  2
          elsif mm.nonzero? then t =  1
          else                   t = -1
          end
        end
        case t
        when -1
          tail = []
          sep = ''
        when 0
          f[:w] -= 2 if f[:w]
          tail = ['%02d' % mm]
          sep = ''
        when 1
          f[:w] -= 3 if f[:w]
          tail = ['%02d' % mm]
          sep = ':'
        when 2
          f[:w] -= 6 if f[:w]
          tail = ['%02d' % mm, '%02d' % ss]
          sep = ':'
        end
        ([emit_z(sign * hh, 2, f)] + tail).join(sep)
      when '%'; emit_a('%', 0, f)
      when '+'; emit_a(strftime('%a %b %e %H:%M:%S %Z %Y'), 0, f)
      when '1'
        if $VERBOSE
          warn("warning: strftime: %1 is deprecated; forget this")
        end
        emit_n(jd, 1, f)
      when '2'
        if $VERBOSE
          warn("warning: strftime: %2 is deprecated; use '%Y-%j'")
        end
        emit_a(strftime('%Y-%j'), 0, f)
      when '3'
        if $VERBOSE
          warn("warning: strftime: %3 is deprecated; use '%F'")
        end
        emit_a(strftime('%F'), 0, f)
      else
        c
      end
    end
  end