Blockeditmode: Control to use REFEDIT or BEDIT to edit the block when double click block
Layerdlgmode: Control the default way when you run LAYER command, set to 1 means load the layer panel, while 0 means to load the classic layer dialog box.
Undosnapshot: Turn on or off the undo / redo preview feature, by default it is turned off to make sure the performance.
Commands:
Sysvdlg: to check the system variable info, including the default value, where to save, and its meaning.