AutoCAD - Flatten geometry to 2D

How many times do you open up a 2D drawing only to notice that the geometry is on different Z levels!

Try this:

Make sure the layers are unlocked

copy and paste these two lines

(command "MOVE" (ssget "x") "" "0,0,0" "0,0,1e99")
(command "MOVE" (ssget "p") "" "0,0,0" "0,0,-1e99")