ode>.
      The second constructor argument for <code class="computeroutput"><span class="identifier">pbase3_type</span></code>
      is a special case of necessary conversion; all forms of the null-pointer literal
      in C++ (except <code class="computeroutput"><span class="keyword">nullptr</span></code> from C++11)
      also look like compile-time integral expressions, so C++ always interprets
      such code as an integer when it has overloads that can take either an integer
      or a pointer. The la