Allow drag and drop interaction to be configured with a source

externs/olx.js

@@ -2710,6 +2710,7 @@ olx.interaction.DoubleClickZoomOptions.prototype.delta;
 
 /**
  * @typedef {{formatConstructors: (Array.<function(new: ol.format.Feature)>|undefined),
+ *     source: (ol.source.Vector|undefined),
  *     projection: ol.ProjectionLike,
  *     target: (Element|undefined)}}
  */
@@ -2724,6 +2725,18 @@ olx.interaction.DragAndDropOptions;
 olx.interaction.DragAndDropOptions.prototype.formatConstructors;
 
 
+/**
+ * Optional vector source where features will be added.  If a source is provided
+ * all existing features will be removed and new features will be added when
+ * they are dropped on the target.  If you want to add features to a vector
+ * source without removing the existing features (append only), instead of
+ * providing the source option listen for the "addfeatures" event.
+ * @type {ol.source.Vector|undefined}
+ * @api
+ */
+olx.interaction.DragAndDropOptions.prototype.source;
+
+
 /**
  * Target projection. By default, the map's view's projection is used.
  * @type {ol.ProjectionLike}