// *** before: ***
const
  MaxBytes = 1073741824;    // is that a gigabyte? count the digits
  Timeout  = 300000;
  Mask     = $FFFF0000;

// *** in version 11: ***
const
  MaxBytes = 1_073_741_824;
  Timeout  = 300_000;
  Mask     = $FFFF_0000;
  Bits     = %1010_1010;

begin
  Writeln(MaxBytes);        // 1073741824 - the value is unchanged

  // the underscore is thrown away by the compiler, so it may stand
  // anywhere inside the literal. It may not start one: _100 is a name
end;