">streams</span><span class="special">::</span><span class="identifier">istream</span></code>
            and <code class="computeroutput"><span class="identifier">concurrency</span><span class="special">::</span><span class="identifier">streams</span><span class="special">::</span><span class="identifier">ostream</span></code> reference parameters. Presumably,
            these are abstract interfaces which may be subclassed by users to achieve
            custom behaviors.
          </li>
<li class="listi