Information on Hook Constants

Anyone can explain what these hooks do? Especially WH_MIN and WH_MAX. http://msdn.microsoft.com/en-us/library/ms644959(VS.85).aspx

  WH_MIN = -1
  WH_MSGFILTER = -1
  WH_JOURNALRECORD = 0
  WH_JOURNALPLAYBACK = 开发者_如何转开发1
  WH_KEYBOARD = 2
  WH_GETMESSAGE = 3
  WH_CALLWNDPROC = 4
  WH_CBT = 5
  WH_SYSMSGFILTER = 6
  WH_MOUSE = 7
  WH_HARDWARE = 8
  WH_DEBUG = 9
  WH_SHELL = 10
  WH_FOREGROUNDIDLE = 11
  WH_CALLWNDPROCRET = 12
  WH_KEYBOARD_LL = 13
  WH_MOUSE_LL = 14
  WH_MAX = 15

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MIN and MAX values like that are usually just there so you know the range of valid numbers