format 01/01/1990 00:00:00:
  a: Mon
  A: Monday
  b: Jan
  B: January
  c: Mon Jan  1 00:00:00 1990
  d: 01
  e:  1
  H: 00
  I: 12
  j: 001
  m: 01
  M: 00
  p: AM
  S: 00
  U: 00
  w: 1
  W: 00
  x: 01/01/90
  X: 00:00:00
  y: 90
  Y: 1990
  Z: +0000
  %: %

format 12/31/2011 23:59:59:
  a: Sat
  A: Saturday
  b: Dec
  B: December
  c: Sat Dec 31 23:59:59 2011
  d: 31
  e: 31
  H: 23
  I: 11
  j: 365
  m: 12
  M: 59
  p: PM
  S: 59
  U: 52
  w: 6
  W: 52
  x: 12/31/11
  X: 23:59:59
  y: 11
  Y: 2011
  Z: +0000
  %: %