("Rulers") Reference Lines cannot be added to the nesting frame

When I make a “son-frame” nested in a “mother-frame”, I’d always like to add reference lines to each frame to arrange the elements. Though, I found that I cannot add this references to a frame(frame 2) which already belongs to a frame(frame 1).

If possible, the reference line could be added to the frame I selected. Or it changes its relationship when I drag and move the reference line to some other “frame area”.