drawBackgroundRect = function drawBackgroundRect(elem, bounds) {
  var rectElem = drawRect(elem, {
    x: bounds.startx,
    y: bounds.starty,
    width: bounds.stopx - bounds.startx,
    height: bounds.stopy - bounds.starty,
    fill: bounds.fill,
    class: 'rect'
  });
  rectElem.lower();
}
Setup node number. The result is appended to the svg.