collapse.js data-parent requires .panel

[dancek]

The collapse js plugin should be made more flexible by not requiring a wrapping .panel for data-parent to work. The "show only one at a time" functionality is useful outside of accordions and without panel-like styling.

Fixing this is as easy as changing the selector in https://github.com/twbs/bootstrap/blob/v3.0.2/js/collapse.js#L51 to something purely semantic that doesn't come with styles -- try > .collapse-group > .in for example.

Also note that the docs do not explicitly mention what the DOM should be for data-parent to work.

See also discussion in #10023.

[cvrebert]

Duplicate of #10966. Please search next time.

[dancek]

I did, but only found #10023 (with your suggestion of creating a new issue, which I did not find). Sorry.