Sample use 1: call ModeMapping( "b", "c", ":echo 'Salman'" ) This means that if GUI is running, b becomes the lhs and the :echo bit becomes the rhs; if no GUI is running, you get c as the lhs instead. Sample use 2: call ModeMapping( "a", "d", ":echo 'Halim'gv", 'vmap ' ) If the GUI is running, a is the lhs, :echo etc. is the rhs and the mapp command used is 'vmap ' (a buffer-specific visual mode mapping). Note that the last argument is optional (and wasn't there in the last example).