Bootstrap 3 how to remove auto-hide of accordion elements when expanding one?

Question

JavaScript

How not to collapse other panels when one is selected?

<div id="accordion" class="panel-group">

                    <div class="panel panel-default">
                        <div class="panel-heading">
                            <h4 class="panel-title">
                                <a class="collapse-toggle" href="#accordion-collapse1" data-toggle="collapse" data-parent="#accordion">
                                    <strong>HEADER1</strong>
                                </a>
                            </h4>
                        </div>

                        <div id="accordion-collapse1" class="in panel-collapse collapse">
                            <div class="panel-body">Content 1</div>
                        </div>
                    </div>

                    <div class="panel panel-default">
                        <div class="panel-heading">
                            <h4 class="panel-title">
                                <a class="collapse-toggle" href="#accordion-collapse2" data-toggle="collapse" data-parent="#accordion">
                                    <strong>HEADER2</strong>
                                </a>
                            </h4>
                        </div>

                        <div id="accordion-collapse2" class="in panel-collapse collapse">
                            <div class="panel-body">Content 2</div>
                        </div>
                    </div>

                    <div class="panel panel-default">
                        <div class="panel-heading">
                            <h4 class="panel-title">
                                <a class="collapse-toggle" href="#accordion-collapse3" data-toggle="collapse" data-parent="#accordion">
                                    <strong>HEADER3</strong>
                                </a>
                            </h4>
                        </div>

                        <div id="accordion-collapse3" class="in panel-collapse collapse">
                            <div class="panel-body">Content 3 </div>
                        </div>
                    </div>


                </div>

Answer 1

getbootstrap.com/javascript/#collapse-options
Options
parent selector false If a selector is provided, then all collapsible elements under the specified parent will be closed when this collapsible item is shown. (similar to traditional accordion behavior - this is dependent on the panel class).
data-parent="#accordion" remove from markup