--- /dev/null
+/**\r
+ * Constructs a new Message ExtensionField.\r
+ * @exports ProtoBuf.Reflect.Message.ExtensionField\r
+ * @param {!ProtoBuf.Builder} builder Builder reference\r
+ * @param {!ProtoBuf.Reflect.Message} message Message reference\r
+ * @param {string} rule Rule, one of requried, optional, repeated\r
+ * @param {string} type Data type, e.g. int32\r
+ * @param {string} name Field name\r
+ * @param {number} id Unique field id\r
+ * @param {!Object.<string,*>=} options Options\r
+ * @constructor\r
+ * @extends ProtoBuf.Reflect.Message.Field\r
+ */\r
+var ExtensionField = function(builder, message, rule, type, name, id, options) {\r
+ Field.call(this, builder, message, rule, /* keytype = */ null, type, name, id, options);\r
+\r
+ /**\r
+ * Extension reference.\r
+ * @type {!ProtoBuf.Reflect.Extension}\r
+ * @expose\r
+ */\r
+ this.extension;\r
+};\r
+\r
+// Extends Field\r
+ExtensionField.prototype = Object.create(Field.prototype);\r