They are applied left to right. You can prove this to yourself by the following example:
block 1 2;1 2;1 2;-1 1 -1 1 -1 1
lct 1 rz 45 mx 10;
lrep 1;
block 1 2;1 2;1 2;-1 1 -1 1 -1 1
lct 1 mx 10 rz 45;
lrep 1;
merge
grid on
la parts
Part 1 remains on the x-axis proving that the rotation was done first.
Part 2 is on the 45 degree diagonal proving the rotation was done second.
