The K4 runtime switch is not documented in Visual COBOL for Visual Studio.
The K4 runtime switch (i.e. COBSW= K4) is a holdover from the old COBOL Workbench product. Although it is not documented in Net Express and Visual COBOL for Visual Studio, it is still a valid COBOL runtime switch.
The purpose of this runtime switch is to cause runtime system error messages to stay on the screen until a key is pressed.
This is useful in batch runs where you want to know if any program terminates with a run-time system error message, or in a system that displays menus, where run-time system error messages can sometimes be quickly overwritten.
The description of this runtime switch has been added to the documentation of Visual COBOL 6.0 for Visual Studio.
Note: This is already available in the documentation of Visual COBOL for Eclipse.