s">[<span name="I">I</span>, <span name="J">J</span>, <span name="O">O</span>]</span><span class="result"> extends <span class="extype" name="scala.AnyRef">AnyRef</span></span>
      </span>
      </h4>
      
          <div id="comment" class="fullcommenttop"><div class="comment cmt"><p>A Stacker operates on two input Index instances and produces a new output Index
whose entries are drawn from the Cartesian product of the elements of the original
indexes, and whose ordering is likewise specified by the ori