ce wrapper of the
element or <i>to another chained pointer</i>; that is, chained pointers are arbitrary
compositions of pointer-like types ultimately dereferencing
to the element from where the key is to be extracted. Examples of chained
pointers to <code>employee</code> are:
<ul>
  <li><code>employee *</code>,</li>
  <li><code>const employee *</code>,</li>
  <li><code>std::unique_ptr&lt;employee></code>,</li>
  <li><code>std::list&lt;boost::reference_wrapper&lt;employee> >::iterator</code>,</li>
  <li><cod