def to_xml_string(str = '')
      str << '<c:view3D>'
      %w(rot_x h_percent rot_y depth_percent r_ang_ax perspective).each do |key|
        str << element_for_attribute(key, 'c')
      end
      str << '</c:view3D>'
    end
DataTypeValidator.validate "#{self.class}.perspective", [Integer], v, lambda {|arg| arg >= 0 && arg <= 240 }; @perspective = v; end
Serializes the object
@param [String] str
@return [String]