code: function (when, len, attrs) {
        var x = time_x(when);
        var end_y = ui.y + len;
        var e = paper.path(
          "M" + x + "," + ui.y + " " +
          "L" + x + "," + end_y
        ).attr(attrs || {});
        return e;    
      }
docs: draw a line at when from y as far as len pixels with attrs.