valor-software/ng2-bootstrap

<p>Be sure to add <code class="highlighter-rouge">aria-expanded</code> to the control element. This attribute explicitly conveys the current state of the collapsible element tied to the control to screen readers and similar assistive technologies. If the collapsible element is closed by default, the attribute on the control element should have a value of <code class="highlighter-rouge">aria-expanded="false"</code>. If you’ve set the collapsible element to be open by default using the <code class="highlighter-rouge">show</code> class, set <code class="highlighter-rouge">aria-expanded="true"</code> on the control instead. The plugin will automatically toggle this attribute on the control based on whether or not the collapsible element has been opened or closed. If the control element’s HTML element is not a button (e.g., an <code class="highlighter-rouge">&lt;a&gt;</code> or <code class="highlighter-rouge">&lt;div&gt;</code>), the attribute <code class="highlighter-rouge">role="button"</code> should be added to the element.</p>
<p>If your control element is targeting a single collapsible element – i.e. the <code class="highlighter-rouge">data-target</code> attribute is pointing to an <code class="highlighter-rouge">id</code> selector – you should add the <code class="highlighter-rouge">aria-controls</code> attribute to the control element, containing the <code class="highlighter-rouge">id</code> of the collapsible element. Modern screen readers and similar assistive technologies make use of this attribute to provide users with additional shortcuts to navigate directly to the collapsible element itself.</p>