In the case that a vertex is inside the rectangle of a !-box, but it is does not have a parent !-box, then we should have a notation informing the user of this, so that confusion can be avoided. A thin red line connecting the corner of the !-box and the vertex in question should be drawn. In addition, text should be displayed next to the line indicating that the vertex is not inside. After (or if) the user removes the vertex from the !-box, then the line and text are no longer displayed.
In the case that a vertex is inside the rectangle of a !-box, but it is does not have a parent !-box, then we should have a notation informing the user of this, so that confusion can be avoided. A thin red line connecting the corner of the !-box and the vertex in question should be drawn. In addition, text should be displayed next to the line indicating that the vertex is not inside. After (or if) the user removes the vertex from the !-box, then the line and text are no longer displayed.