property dragHovered

This property returns if a drag operation is in progress, the mouse cursor is over this box. This box would be the target of the drop (if one was to occur) while this property is true.

var bx = scene.getBoxById("customBox");
var msgBx = scene.getBoxById("msgBox");

if (bx && msgBx && bx.draggedHovered)
    msgBx.label = "Current Target Drop Box Is: " + bx.id;