def subtable(cell_options = {}, options = {}, &block)
      raise StandardError.new('subtable called outside of row block') unless @in_row
      cell cell_options || {} do
        PdfTableBuilder.new(@doc, options || {}, &block).to_table
      end
    end
def subtable(cell_options = {}, options = {}, &block)
      raise StandardError.new('subtable called outside of row block') unless @in_row
      cell cell_options || {} do
        PdfTableBuilder.new(@doc, options || {}, &block).to_table
      end
    end
Builds a subtable within the current row.

 The +cell_options+ are passed to the current cell.
 The +options+ are passed to the new TableBuilder.