ator is
        a templated class configurable using policies. The description of <code class="computeroutput"><span class="identifier">multi_pass</span></code> above is how it was originally
        implemented (before it used policies), and is the default configuration now.
        But, <code class="computeroutput"><span class="identifier">multi_pass</span></code> is capable
        of much more. Because of the open-ended nature of policies, you can write
        your own policy to make <code class="compu