diff -r 000000000000 -r 6474c204b198 addon-sdk/source/lib/sdk/ui/sidebar/contract.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/addon-sdk/source/lib/sdk/ui/sidebar/contract.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,27 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+* License, v. 2.0. If a copy of the MPL was not distributed with this
+* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+'use strict';
+
+const { contract } = require('../../util/contract');
+const { isValidURI, URL, isLocalURL } = require('../../url');
+const { isNil, isObject, isString } = require('../../lang/type');
+
+exports.contract = contract({
+  id: {
+  	is: [ 'string', 'undefined' ],
+  	ok: v => /^[a-z0-9-_]+$/i.test(v),
+    msg: 'The option "id" must be a valid alphanumeric id (hyphens and ' +
+         'underscores are allowed).'
+  },
+  title: {
+  	is: [ 'string' ],
+  	ok: v => v.length
+  },
+  url: {
+    is: [ 'string' ],
+    ok: v => isLocalURL(v),
+    map: function(v) v.toString(),
+    msg: 'The option "url" must be a valid local URI.'
+  }
+});