added optional groups to route syntax, with tests

backbone.js

@@ -894,9 +894,10 @@
 
   // Cached regular expressions for matching named param parts and splatted
   // parts of route strings.
+  var optionalParam = /\((.*?)\)/g;
   var namedParam    = /:\w+/g;
   var splatParam    = /\*\w+/g;
-  var escapeRegExp  = /[-[\]{}()+?.,\\^$|#\s]/g;
+  var escapeRegExp  = /[-{}[\]+?.,\\^$|#\s]/g;
 
   // Set up all inheritable **Backbone.Router** properties and methods.
   _.extend(Router.prototype, Events, {
@@ -947,6 +948,7 @@
     // against the current location hash.
     _routeToRegExp: function(route) {
       route = route.replace(escapeRegExp, '\\$&')
+                   .replace(optionalParam, '(?:$1)?')
                    .replace(namedParam, '([^\/]+)')
                    .replace(splatParam, '(.*?)');
       return new RegExp('^' + route + '$');

index.html

@@ -1931,15 +1931,27 @@ <h2 id="Router">Backbone.Router</h2>
       similar to the <a href="#View">View</a>'s <a href="#View-delegateEvents">events hash</a>.
       Routes can contain parameter parts, <tt>:param</tt>, which match a single URL
       component between slashes; and splat parts <tt>*splat</tt>, which can match
-      any number of URL components.
+      any number of URL components. Part of a route can be made optional by
+      surrounding it in parentheses <tt>(/:optional)</tt>.
     </p>
 
     <p>
       For example, a route of <tt>"search/:query/p:page"</tt> will match
       a fragment of <tt>#search/obama/p2</tt>, passing <tt>"obama"</tt>
-      and <tt>"2"</tt> to the action. A route of <tt>"file/*path"</tt> will
-      match <tt>#file/nested/folder/file.txt</tt>,
-      passing <tt>"nested/folder/file.txt"</tt> to the action.
+      and <tt>"2"</tt> to the action.
+    </p>
+
+    <p>
+      A route of <tt>"file/*path"</tt> will match
+      <tt>#file/nested/folder/file.txt</tt>, passing
+      <tt>"nested/folder/file.txt"</tt> to the action.
+    </p>
+
+    <p>
+      A route of <tt>"docs/:section(/:subsection)"</tt> will match
+      <tt>#docs/faq</tt> and <tt>#docs/faq/installing</tt>, passing
+      <tt>"faq"</tt> to the action in the first case, and passing <tt>"faq"</tt>
+      and <tt>"installing"</tt> to the action in the second.
     </p>
 
     <p>

test/router.js

@@ -69,6 +69,7 @@ $(document).ready(function() {
       "contacts":                   "contacts",
       "contacts/new":               "newContact",
       "contacts/:id":               "loadContact",
+      "optional(/:item)":           "optionalItem",
       "splat/*args/end":            "splat",
       "*first/complex-:part/*rest": "complex",
       ":entity?*args":              "query",
@@ -105,6 +106,10 @@ $(document).ready(function() {
       this.contact = 'load';
     },
 
+    optionalItem: function(arg){
+      this.arg = arg !== undefined ? arg : null;
+    },
+
     splat : function(args) {
       this.args = args;
     },
@@ -199,6 +204,15 @@ $(document).ready(function() {
     equal(router.args, 'long-list/of/splatted_99args');
   });
 
+  test("routes (optional)", 2, function() {
+    location.replace('http://example.com#optional');
+    Backbone.history.checkUrl();
+    equal(router.arg, null);
+    location.replace('http://example.com#optional/thing');
+    Backbone.history.checkUrl();
+    equal(router.arg, 'thing');
+  });
+
   test("routes (complex)", 3, function() {
     location.replace('http://example.com#one/two/three/complex-part/four/five/six/seven');
     Backbone.history.checkUrl();