Peter N. Lewis pointed me to the following:
{$methods-always-virtual} {allowed} {$no-methods-always-virtual} {error message} program P; begin end.
GPC accepts {$methods-always-virtual} as a directive in source code, but it rejects {$no-methods-always-virtual}. Is there a special reason why ? The value of the flag changes also (I think) when switching from {$mac-pascal} to {$gnu-pascal}.
Regards,
Adriaan van Os