function() {
      //console.log(d3.event)
      if (d3.event.wheelDeltaY > 0) step(-1);
      if (d3.event.wheelDeltaY < 0) step(1);
  });
  d3.select(this.contentWindow).on("keydown", function() {
      //console.log(d3.event.keyCode)
    switch (d3.event.keyCode) {
      case 39: // right arrow
      case 32: // space
      case 34: { // page down
        step(+1);
        break;
      }
      case 8: { // delete
        step(d3.event.shiftKey ? +1 : -1);
        break;
      }
      case 37: // left arr