+function DygraphLayout() {}
+
+/**
+ * @type {Array}
+ */
+DygraphLayout.prototype.datasets;
+
+// TODO: DygraphOptions should not reach inside Dygraph private data like this.
+/** @type {Object} */
+Dygraph.prototype.attrs_;
+/** @type {Object} */
+Dygraph.prototype.user_attrs_;
+
+/**
+ * @type {DygraphLayout}
+ */
+Dygraph.prototype.layout_;
+
+/** @type {function(): string} */
+Dygraph.prototype.getHighlightSeries;