pan class="identifier">get</span></code>. The message
                  body becomes valid before entering this function, and remains valid
                  until the writer is destroyed. The function will ensure that <code class="computeroutput"><span class="special">!</span><span class="identifier">ec</span></code>
                  is <code class="computeroutput"><span class="keyword">true</span></code> if there was
                  no error or set to the appropriate error code if there was one.
      