code: def to_rtf
           text   = StringIO.new
           temp   = StringIO.new
           offset = 0
  
           text << "\\trowd\\tgraph#{parent.cell_margin}"
           self.each do |entry|
              widths = entry.border_widths
              colour = entry.shading_colour
  
              text << "\n"
              text << "\\clbrdrt\\brdrw#{widths[0]}\\brdrs" if widths[0] != 0
              text << "\\clbrdrl\\brdrw#{widths[3]}\\brdrs" if widths[3] != 0
              text << "\\clbrdrb\\brdrw#{widths[2]}\\brdrs" if widths[2] != 0
              text << "\\clbrdrr\\brdrw#{widths[1]}\\brdrs" if widths[1] != 0
              text << "\\clcbpat#{root.colours.index(colour)}" if colour != nil
              text << "\\cellx#{entry.width + offset}"
              temp << "\n#{entry.to_rtf}"
              offset += entry.width
           end
           text << "#{temp.string}\n\\row"
  
           text.string
        end
docs: This method overloads the store method inherited from the ContainerNode
   class to forbid addition of further nodes.
  
   ==== Parameters
   node::  A reference to the node to be added.
  def store(node)
     RTFError.fire("Table row nodes cannot have nodes added to.")
  end
   This method generates the RTF document text for a TableCellNode object.