A.5.304 STR: Store Task Register
STR r/m16 ; 0F 00 /1 [286,PRIV]
STR stores the segment selector corresponding to the contents of the
Task Register into its operand. When the operand size is 32 bit and the
destination is a register, the upper 16-bits are cleared to 0s. When the
destination operand is a memory location, 16 bits are written regardless
of the operand size.