lib/spreadsheet/format.rb
def rotation=(rot)
      if rot.to_s.downcase == 'stacked'
        @rotation_stacked = true
        @rotation = 0
      elsif rot.kind_of?(Integer)
        @rotation_stacked = false
        @rotation = rot % 360
      else
        raise TypeError, "rotation value must be an Integer or the String 'stacked'"
      end
    end
def rotation=(rot)
      if rot.to_s.downcase == 'stacked'
        @rotation_stacked = true
        @rotation = 0
      elsif rot.kind_of?(Integer)
        @rotation_stacked = false
        @rotation = rot % 360
      else
        raise TypeError, "rotation value must be an Integer or the String 'stacked'"
      end
    end
Set the Text rotation
 Valid values: Integers from -90 to 90,
 or :stacked (sets #rotation_stacked to true)