place
Position this child at x, y relative to this container's top-left.
Paint order is declaration order: two children that overlap are drawn in the order the container declared them, not the order they were placed in here.
Throws
if this child has already been placed, since one of the two positions would be discarded
if this placeable's child index is out of range for this container. That is how a placeable belonging to another container is caught, though only when its index happens to fall outside this one's.