# File lib_wpm/wpm.rb, line 1887
    def check_mapping
      if (! @action && ! @page && ! @href) then
        raise PropertyError, "required `action', `page' or href property at #{widget_id.inspect}"
      end
      if (@action && @target) then
        raise PropertyError, "conflicted action and target property at #{widget_id.inspect}"
      end

      nil
    end