Collapsible `parent` option is dependent on dom structure

Created by: steodor

Hi, i found this pull request: https://github.com/twbs/bootstrap/pull/7600

In the latest version i see that the parent option is now dependent on the .panel class, i.e.:

var actives = this.$parent && this.$parent.find('> .panel > .in')

Why don't you just leave it like it was (.collapse.in) or better yet, just:

var actives = this.$parent && this.$parent.find('.in')

Or, i get it if the parent must have a class, to avoid conflicts with other libraries, but can you please explain what's up with depending on dom structure? (the double > in the selector really don't look good to me)

Oh and, the docs are way behind on this one. There's an .accordion-group class mentioned, but not saying how it should be used, and the example doesn't have one at all (yet it works, probably on an old bootstrap version).

So basically, please decide on a structure and update the docs & examples accordingly. If you want i could help you with some of the workload, as you see fit.

Thank you.