$MODE : Set compiler compatibility mode

The {$MODE} sets the compatibility mode of the compiler. This is equivalent to setting one of the command-line options -So, -Sd, -Sp or -S2. it has the following arguments:

Default
Default mode. This reverts back to the mode that was set on the command-line.
Delphi
Delphi compatibility mode. All object-pascal extensions are enabled. This is the same as the command-line option -Sd.
TP
Turbo pascal compatibility mode. Object pascal extensions are disabled, except ansistrings, which remain valid. This is the same as the command-line option -So.
FPC
FPC mode. This is the default, if no command-line switch is supplied.
OBJFPC
Object pascal mode. This is the same as the -S2 command-line option.
GPC
GNU pascal mode. This is the same as the -Sp command-line option.

For an exact description of each of these modes, see appendix D, on page 510.