local m.x
m.x=home((1)+"dv_foxhelp.chm"
set help to m.x

this is set by default with help installation and Specifies a default Help file that is displayed when you press F1 or issue HELP.
can dynamically specify another help file with this mecanism.

" set help off":
Makes Visual FoxPro online Help unavailable.any help is fired when pressing F1 key