# File lib_wpm/wpm.rb, line 2746
    def check_mapping
      unless (@value) then
        raise PropertyError, "required `value' property at #{widget_id.inspect}"
      end

      case (@data_type)
      when 'string', 'integer', 'float'
        # nothing to do.
      else
        raise PropertyError, "unknown property value #{@data_type.inspect} of data-type"
      end

      nil
    end