title: How to document friend injection functionality with doxygen?
body: <p>Given some code like in the following example:</p>
  
  <pre><code>class MyClass;
  
  class Injector {
      /**
       * @brief MyClass addition.
       */
      friend MyClass operator+(MyClass a, MyClass b) { ... }
  };
  
  class MyClass: private Injector {};
  </code></pre>
  
  <p>How can I make doxygen include the documentation of <code>operator+()</code> on the documentation page of the MyClass class? Functionally it clearly belongs there. Is there some general way to make doxygen document functionality available through ADL?</p>
  
  <p>A useful example in the real world: I'd like doxygen to include operators provided by the base classes in <code>boost/operators.hpp</code>.</p>