With many converters and displayers extra parameters can be specified. Many of these are specific to the displayer or converter and details are in other documentation.
All fields can be specified as "required". If this is checked then a value must be specified in the field. Try checking required in the "MyFirstField" and testing the field. You can not click OK until a value is specified.

In addition many converters can have regular expressions, which allow more complex validation rules to be specified. More details on common regular expressions can be found at regular expression library.
Try adding the regular expression ^[0-9]$ to "MyFirstField". It requires that the entry in the field is a one digit number.
Changing the regular expression to ^[0-9]+$ requires that the entry in the field is a multi-digit number.