We use `'section[id^="' + panel.id + '-"]'` to find all sub panels of a panel and which requires the ID of the sub panels follows the rule. 
In this patch `data-require-sub-panels` works well as it is only added to the second level panels. The naming of deeper level panels may not follow the rule. Suggest to leave a comment here describing the behavior in case others would like to use `data-require-sub-panels` in newly created or deeper level panels.