anchor.diff:  
   == Reuse
   You may find yourself defining the same options, parameters or command attributes in many command line applications.
  -To reduce duplication, picocli supports both subclassing and mixins as ways to reuse such options and attributes.
  +To reduce duplication, picocli supports two ways to reuse such options and attributes: subclassing and mixins.
   
   === Subclassing
  -One way to reuse the above option and attributes is to extend the class.
  +One way to reuse options and attributes is to extend the class where they are defined.
   Picocli will walk the class hierarchy to check for annotations, so `@Options`, `@Parameters` and `@Command` attributes declared on a superclass are available in all subclasses.
   
   Below is an example class, `ReusableOptions`, that defines some usage help attributes and a `--verbose` option that we want to reuse.
  
positive.code:     private ReusableOptions myMixin;
  
      @Command
      void subzip(@Mixin ReusableOptions opts) {
          // ...
      }
  }
  
negative.code: ----
  
  === Mixins
  Picocli 3.0 introduced the concept of "mixins".
  Mixins allow reuse without subclassing:
  picocli annotations from _any_ class can be added to ("mixed in" with) a command.
  Picocli's <<Mixin Standard Help Options,mixinStandardHelpOptions>> internally uses a mixin.
  
  A mixin is a separate class with options, positional parameters, subcommands and command attributes that you want to reuse in one or more other commands.
  A command receiving these mixed in options, positional parameters, and command attributes is called a "mixee".
  
  Mixins can be installed declaratively with a `@Mixin`-annotated field (or a `@Mixin`-annotated method parameter for command methods).
  Alternatively, mixins can be installed programmatically by calling the `CommandLine.addMixin` method with an instance of the mixin class.
  
  The examples below again use the sample `ReusableOptions` class as the mixin:
  
  