Bits: 0-1 - Interpreted similarly to R0 bits 8 & 9 for OS_SpriteOp:
0 - Use sprite name (R6) and Wimp sprite pool.
1 - Use sprite name (R6) and sprite area pointer (R5).
2 - Use sprite pointer (R6) and sprite area pointer (R5).
3 - Invalid value
2 - Plot sprite at half size.
3 - Ensure new item is visible by scrolling the list. (TextGadgets 0.19)
4-7 - Left indent in steps of 32 OS units (value 0-15). (TextGadgets 0.85)
