How can I select the next caster group in StarCraft 2?

If I have a big group of units selected, and two or more of the unit types can cast spells, how can I switch groups without de-selecting my units?

From gaming Mark

• With the TAB key. You will go to the next group of units. SHIFT+Tab will go the opposite direction (so, previous group of units)

  Mark : I'll assume this works... I just remember having this problem in beta, but I haven't had the chance to pick up a retail copy yet! (I'm on vacation..and here I am thinking "i cant wait to get back home so I can play some sc2")

  Oak : Just a comment - it works the same way in Warcraft III, the previous Blizzard RTS.

  Raven Dreamer : Thanks for confirming Shift+Tab, McKay!

  Mag Roader : Note that Shift+Tab is also the Steam Overlay hotkey. If you're using Steam (as I am) you may want to consider remapping that (or remapping StarCraft's keys).
  From Raven Dreamer