You can clone with
HTTPS or Subversion.
Collapsibles (both single and grouped) don't feel as responsive as we'd ideally like. We have to use mouse events here to avoid the double tap phenomenon because opening and closing these shifts the layout enough to cause touch/mouse een mis-matches.
To make things feel a bit mor responsive, I think we should borrow the active state logic from lists since it's a similar situation: we flip to the active state on tap, but bind to click to the actual collapse action. This will at least provide visual feedback while we're waiting for the click to happen.
Fixes #4220 - Collapsible - add active state on tap
How fixed: Added the active button state on tap of a collapsible heading
How Tested: Docs and http://jsbin.com/omacox/100