This mode is selected by the $MODE FPC switch. On the command line, this means that you use none of the other compatibility mode switches. It is the default mode of the compiler (-Mfpc). This means essentially:
You must use the address operator to assign procedural variables.
A forward declaration must be repeated exactly the same by the implementation of a function/procedure. In particular, you cannot omit the parameters when implementing the function or procedure.
Overloading of functions is allowed without overload modifier.
Nested comments are allowed.
The Objpas unit is NOT loaded.
You can use the cvar type.
PChars are converted to strings automatically.
Strings are shortstrings by default.