Group definitions can be used to define texture animations such as the animated water in Doom. Alternatively they can also be used to tell the engine to cache all the textures of a group at the same time (e.g., switch textures) if they are likely to be needed quickly.

One Group definition can only include Flat blocks or Texture blocks only.

<Copy> Group
{
	 Flags = flaga | flagb | flagc etc...
		  # smooth: Interpolate/blend texture transitions.
		  #
		  # first_only: Only animate if the texture used in the map is the first
                  #             texture defined in this sequence.
                  #
		  # precache: Cache all textures in this sequence at once.

	 Flat
	 {
		  ID = ""
		  # Name of the Flat lump eg FWATER1

		  Tics = integer
		  # How many tics to wait before moving onto the next Flat in the group
		  # One second is equal to 35 Tics.

		  Random = integer
		  # How many additional randomized tics to wait before moving onto the
		  # next Flat in the group
		  # One second is equal to 35 Tics.
	 }

	 Texture
	 {
		  ID = ""
		  # Name of the Texture lump eg SLADRIP1

		  Tics = integer
		  # How many tics to wait before moving onto the next Texture in the group
		  # One second is equal to 35 Tics.

		  Random = integer
		  # How many additional randomized tics to wait before moving onto the
		  # next Flat in the group
		  # One second is equal to 35 Tics.
	 }
}

Group {
  Flags = smooth
  Flat { ID = "FWATER1" Tics = 8 }
  Flat { ID = "FWATER2" Tics = 8 }
  Flat { ID = "FWATER3" Tics = 8 }
  Flat { ID = "FWATER4" Tics = 8 }
}

Group {
  Flags = smooth
  Texture { ID = "BLODGR1" Tics = 8 }
  Texture { ID = "BLODGR2" Tics = 8 }
  Texture { ID = "BLODGR3" Tics = 8 }
  Texture { ID = "BLODGR4" Tics = 8 }
}