Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/modules/contextual/js/views/RegionView.js

@@ -0,0 +1,53 @@
+/**
+ * @file
+ * A Backbone View that renders the visual view of a contextual region element.
+ */
+
+(function (Drupal, Backbone, Modernizr) {
+
+  "use strict";
+
+  Drupal.contextual.RegionView = Backbone.View.extend(/** @lends Drupal.contextual.RegionView# */{
+
+    /**
+     * @return {object}
+     */
+    events: function () {
+      var mapping = {
+        mouseenter: function () { this.model.set('regionIsHovered', true); },
+        mouseleave: function () {
+          this.model.close().blur().set('regionIsHovered', false);
+        }
+      };
+      // We don't want mouse hover events on touch.
+      if (Modernizr.touch) {
+        mapping = {};
+      }
+      return mapping;
+    },
+
+    /**
+     * Renders the visual view of a contextual region element.
+     *
+     * @constructs
+     *
+     * @augments Backbone.View
+     */
+    initialize: function () {
+      this.listenTo(this.model, 'change:hasFocus', this.render);
+    },
+
+    /**
+     * @inheritdoc
+     *
+     * @return {Drupal.contextual.RegionView}
+     */
+    render: function () {
+      this.$el.toggleClass('focus', this.model.get('hasFocus'));
+
+      return this;
+    }
+
+  });
+
+})(Drupal, Backbone, Modernizr);