What is const void?
<p>The description of <a href="http://en.cppreference.com/w/cpp/types/is_void" rel="noreferrer"><code>std::is_void</code></a> states that:</p>

<blockquote>
  <p>Provides the member constant value  that is equal to true, if T is the <strong>type void, const void, volatile
  void,</strong> or const volatile void.</p>
</blockquote>

<p>Then what could be <code>const void</code>, or a <code>volatile void</code> ? </p>

<p><a href="https://stackoverflow.com/a/28707034/264325">This answer</a> states that <code>const void</code> return type would be invalid (however compiles on VC++ 2015)</p>

<pre><code>const void foo() { }
</code></pre>

<p>If by standard, <code>const void</code> is invalid (VC being wrong) - then what is <code>const void</code>?</p>