title: A query regarding allocator rebind
body: <p>Under <a href="http://en.cppreference.com/w/cpp/concept/Allocator#Allocator_completeness_requirements" rel="nofollow noreferrer">C++ concepts: Allocator</a></p>
  
  <p>would like some clarity on the following:</p>
  
  <blockquote>
    <p>A::template rebind::other (optional<a href="http://en.cppreference.com/w/cpp/concept/Allocator#Allocator_completeness_requirements" rel="nofollow noreferrer">1</a>)</p>
    
    <p>Notes: <a href="http://en.cppreference.com/w/cpp/concept/Allocator#Allocator_completeness_requirements" rel="nofollow noreferrer">1</a> rebind is only optional (provided by <code>std::allocator_traits</code>)
    if this allocator is a template of the form <code>SomeAllocator&lt;T, Args&gt;</code>,
    where <code>Args</code> is zero or more additional template parameters.</p>
  </blockquote>
  
  <p>Why would <code>rebind</code> be optional in the above case?</p>