A command can have parameters that must be coded (required parameters) and parameters that do not have to be coded (optional parameters).
Optional parameters are usually assigned a system-defined default value if another value is not specified for the parameter when the command is entered.
A command can also have key parameters which are the only parameters shown on the display when a user prompts for the command. After values are entered for the key parameters, the remaining parameters are shown with actual values instead of the default values (such as *SAME or *PRV).