Draw a border around valid regions of a Plot?
If the Border value of a Plot is non-zero, then this border will be drawn as part of the grid. Otherwise, the border is not drawn (although axis labels and tick marks will still appear, unless other relevant Plot attributes indicate that they should not). The default behaviour is to draw the border if tick marks and numerical labels will be drawn around the edges of the plotting area (see the Labelling attribute), but to omit it otherwise.