No-relative-placement partial blockage如何指定relative placement groups？

create_placement_blockage -bbox {10 20 100 200} \
-type partial -blocked_percentage 0 -no_rp_group
-no_rp_group是如何起作用的?作用在哪里啊?
userguide上说会把relative placement groups给exclude，但是怎么定义他们啊?

rp group没用过，还