In a frozen window, certain other highlighting features may appear. In particular rulers and the viewport location indicators as used by the Show Location function will be displayed. Also, the outlines of selected objects will appear in these windows.
Frozen sub-windows have an additional feature: frozen sub-windows display the viewport of the main window, the reverse of the Show Location function for sub-windows (which displays sub-window viewports in the main window).
This allows a useful trick for viewing huge cells. Suppose that one has a large design which takes a long time to render, and one wishes to examine a small part of this design (the approximate coordinates are known). One can employ the following procedure. Freeze the main window and read in the design. Bring up a sub-window by clicking twice outside of the cell boundary, so that the sub-window is empty. Freeze the sub-window, then press the Home key with the cursor in the sub-window to center and fully view the top cell boundary. Use the grid and/or rulers to determine the region of interest. Drag with button 3 to define a rectangle in the sub-window surrounding the region of interest, then click with button 3 in the center of the main window. Un-freeze the main window, and this region will be displayed. The region shown in the main window is shown with a dotted yellow outline in the frozen sub-window.