Question: PlotExpression in mini course not working?

This is one is for Edgardo: In the "mini course", there is a command "PlotExpression" used that does not seem to do anything, at least for me. This is in a fresh Maple 18.01 installation on Linux with the latest version of Physics pulled off the Web today.

I cannot find any reference to PlotExpression in the Maple Help files, so where is this thing supposed to be defined? I >am< running a .mapleinit file of my own, configuring some of the plots[setoptions] parameters to my liking, but it should not clobber anything from the system mapleinit.

Another person managed to get the definition of PlotExpression and send it to me. From that I can see that the underlying plots:-plotcompare command seems to work, at least in part.

???

USPAS