Multiple open panels is definitely feasible. I inspected the code of _clickHandler() and the logic of opening active panels & closing others is within there.
We could check for an option allowing multiple open panels (maybe multipleOpen).
What option would enable this and we would have to decide how it interacts with the collapsible option. We could allow an extra value for collapsible, "multi" for instance. It could be a little confusing however because it's not technically "multi collapsible" but "multi openable". If it were a new option, it could override collapsible. I don't know what to title the option.
On another note, these are some reasons you may want to allow multiple panes to be visible at a time:
- Detail panes provide context for one another
- The vertical height of the accordion area is not fixed
- Different panels of content may be different heights
(from __Designing Web Interfaces__ by Bill Scott & Theresa Neil. Published by O'Reilly 2009)
We could leave it to the user to disable autoHeight & enable clearStyle in order for the design pattern outlined above to be followed or force it upon them.
I'll start working on this and submit some code for review when I'm finished.