    limitation on default-construction.
          </li>
<li class="listitem">
            No stateful allocator support. This follows from the previous limitation
            on default-construction. Buffers for start-line strings must be managed
            externally from the message object since they are not members.
          </li>
<li class="listitem">
            The trailers are stored in a separate object. Aside from the combinatorial
            explosion of the number of additional constructors ne