/**
 * @license
 * Copyright (c) 2016 The Polymer Project Authors. All rights reserved.
 * This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
 * The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
 * The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
 * Code distributed by Google as part of the polymer project is also
 * subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
 */

export class ImportDescriptor {
  type: 'html-import' | 'html-script' | 'html-style' | string;
  url: string;

  constructor(type: string, url: string) {
    this.type = type;
    this.url = url;
  }
}

/**
 * @license
 * Copyright (c) 2016 The Polymer Project Authors. All rights reserved.
 * This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
 * The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
 * The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
 * Code distributed by Google as part of the polymer project is also
 * subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
 */
 
export class ImportDescriptor {
  type: string;
  url: string;

  constructor(type: string, url: string) {
    this.type = type;
    this.url = url;
  }
}

--- 
+++ 
@@ -7,9 +7,9 @@
  * Code distributed by Google as part of the polymer project is also
  * subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
  */
- 
+
 export class ImportDescriptor {
-  type: string;
+  type: 'html-import' | 'html-script' | 'html-style' | string;
   url: string;
 
   constructor(type: string, url: string) {
Add known values to the type of ImportDesriptor.type as documentation.