anchor.diff:  Single-value `@Parameters` are always mandatory, because single-value positional parameters <<Positional Parameter Arity,have `arity = "1"`>> by default.
   
   The `arity` attribute can be used to make multi-value `@Parameters` mandatory:
  -[source, java]
  +
  +.Java
  +[source,java,role="primary"]
   ----
   class BothOptionAndParametersMandatory {
       @Parameters(arity = "1..*", description = "at least one File")
  
positive.code:     File[] files;
  }
  ----
  The following command line arguments would result in an exception complaining that `number` is missing:
  ----
  // invalid: missing option -n
  
negative.code: == Required Arguments
  === Required Options
  Options can be marked `required` to make it mandatory for the user to specify them on the command line. When a required option is not specified, a `MissingParameterException` is thrown from the `parse` method. For example:
  
  .Java
  [source,java,role="primary"]
  ----
  class MandatoryOption {
      @Option(names = "-n", required = true, description = "mandatory number")
  