Add top border to PlotBand
When plotting a plodBand it doesn't plot the top border, if it's required to not plot the top border for some use cases, there should be an option to plot or not the top border.
The plot bands are only single shapes so we can’t currently give them individual borders. What you can do is to add a plotLine at the top value of the plot band.
I get if you can't give them single borders, but once you set the borders, it should be applied to all 4 sides of the band.
As you can see here: http://jsfiddle.net/8bkL6pty/1/ it doesn't apply to to the top of the band when the band is on the xAxis and it doesn't apply to the left of the band when it's on the yAxis.