code: def bottom_border_width=(width)
           size = width.nil? ? 0 : width
           if size > 0
              @borders[BOTTOM] = size.to_i
           else
              @borders[BOTTOM] = nil
           end
        end
docs: This method assigns a border width to the bottom side of a table cell.
   Negative values are ignored and a value of 0 switches the border off.
  
   ==== Parameters
   width::  The new border width setting.