How to model a mixin in UML
<p>What is the best way to represent a "mixin" using UML?</p>

<p>As documented in <a href="https://dzone.com/articles/mixins-pure-java" rel="nofollow">this article</a>:</p>

<blockquote>
  <p>In object-oriented programming languages, a mixin refers to a defined
  amount of functionality which can be added to a class. An important
  aspect of this is that it makes it possible to concentrate more on the
  properties of a particular behaviour than on the inheritance
  structures during development.</p>
</blockquote>

<p>I will give more details about my particular use case.
I have a collection of classes that model different types of objects. Because all of them can be stored on a storage, I want to use a mixin to implement all the functionality related to "being stored".
Of course, I can use abstract classes but I do not like it because these classes should be part of a different hierarchy of classes and the fact that they can be stored is only a secondary property.
Another option can be to use composition and add the "storage node" as a field of this classes. I do not like this option either for the same reason: I do not want to create any dependency between the classes and the storage. </p>

<p>I have already implemented the solution in Java using a mixin based on dynamic proxies and I would like to document the solution with a clear UML class diagram. Is there a standard way to represent this mixin?</p>

<p>I am also wondering whether it is a good idea to model also how the mixin has been implemented (using proxies) or it is better to use a more abstract representation. </p>

<p>Thanks </p>