ol.layer.AnimatedCluster is a layer that animates clusters on zoom change.
The layer is created with an ol.source.Cluster as standard cluster vector layers.
ol.interaction.SelectCluster is a select interaction.
On select cluster springs apart to reveal the features.
The revealed features are themselves selectable.
Revealed features are themselves a cluster with an attribute 'features' that contain the original feature.
The example uses the convex envelope calculation to draw a polygon around the points of the cluster
(see ol-ext convex hull example).