Twitter-bootstrap collapse plugin – how to enable multiple “groups” to be opened?

Just don’t use data-parent attributes:

<div class="accordion" id="accordion2">
  <div class="accordion-group">
    <div class="accordion-heading">
      <a class="accordion-toggle" data-toggle="collapse" href="#collapseOne">
        Collapsible Group Item #1
      </a>

    </div>
    <div id="collapseOne" class="accordion-body collapse in">
      <div class="accordion-inner">Item 1 Body</div>
    </div>
  </div>
  <div class="accordion-group">
    <div class="accordion-heading"> 
      <a class="accordion-toggle" data-toggle="collapse" href="#collapseTwo">
        Collapsible Group Item #2
      </a>
    </div>
    <div id="collapseTwo" class="accordion-body collapse">
      <div class="accordion-inner">Item 2 Body</div>
    </div>
  </div>
</div>

http://jsfiddle.net/HJf6j/2/