anchor.diff:  
   For example:
   
  -[source, java]
  +.Java
  +[source, java,role="primary"]
   ----
   class FallbackValueDemo implements Runnable {
       @Option(names = "-x", arity = "0..1",
  
positive.code: === Default Provider
  Finally, you can specify a default provider in the `@Command` annotation:
  
  [source,java]
  ----
  @Command(defaultValueProvider = MyDefaultProvider.class)
  class MyCommand // ...
  ----
  
  
negative.code: The recommended way to give an option or positional parameter a default value is to use the `defaultValue` annotation attribute. This works correctly with argument groups, `@Option` and `@Parameters`-annotated methods, and allows annotation processors to detect and use default values.
  
  For <<option-parameters-methods,@Option and @Parameters-annotated methods>> and <<command-methods,@Command-annotated methods>>, there is no alternative but to use the `defaultValue` annotation attribute. For example, for an annotated interface:
  
  .Java
  [source,java,role="primary"]
  ----
  interface Spec {
      @Option(names = "-c", defaultValue = "123", description = "... ${DEFAULT-VALUE} ...")
      int count();
  }
  ----
  
  .Kotlin
  [source,kotlin,role="secondary"]
  ----
  interface Spec {
      @Option(names = ["-c"], defaultValue = "123", description = ["... \${DEFAULT-VALUE} ..."])
      fun count(): Int
  }
  ----
  
  Example of using the `defaultValue` attribute in the option of a command method:
  
  .Java
  [source,java,role="primary"]
  ----
  class CommandMethod {
      @Command(description = "Do something.")
  