m-api-collapsible-content"><div class="qm-api-item-content"><div class="qm-api-description"><div class="qm-html-paragraph">The default behaviour of views is to match data and elements up by index (position in the array, and position in the dom tree). This can be changed by providing a function to key upon. This allows you to ensure that data is always linked to the same node between calls of apply(), even if the data being supplied is ordered differently. The key function takes an object from the data array