double zPosition

The draw order of this node compared to its parent and its siblings.

By default nodes are drawn in the order that they have been added to a parent. To override this behavior the zPosition property can be used. A higher value of this property will force the node to be drawn in front of siblings that have a lower value. If a negative value is used the node will be drawn behind its parent.

nodeInFront.zPosition = 1.0;
nodeBehind.zPosition = -1.0;

Source

double get zPosition => _zPosition;
void zPosition=(double zPosition)

Source

set zPosition(double zPosition) {
  assert(zPosition != null);
  _zPosition = zPosition;
  if (_parent != null) {
    _parent._childrenNeedSorting = true;
  }
}