Currently there are six parameters, initially all unfrozen.
XSPEC> freeze 2 ! Parameter 2 is frozen.
XSPEC> freeze 4-6 ! Parameters 4, 5, and 6 are frozen.
XSPEC> thaw 2 3-5 ! Parameters 2, 4, and 5 are thawed, parameter
3 is unaffected.
XSPEC> freeze ! Parameters 3,4,5 are frozen (the last
range input by a freeze or thaw command).