Added page on include/extend.

site/src/layouts/application.haml

@@ -21,7 +21,7 @@
           %li
             =link 'Mixins', '/mixins.html'
           %li
-            =link '<tt>include</tt>/<tt>extend</tt>', '/includeextend.html'
+            =link '<tt>include</tt> and <tt>extend</tt>', '/includeextend.html'
           %li
             =link 'Type checking and the class tree', '/types.html'
       #footer

site/src/pages/includeextend.haml

@@ -0,0 +1,46 @@
+:textile
+  h3. @include@ and @extend@
+
+  The @include@ and @extend@ directives (see "Mixins":/mixins.html) are available as static methods
+  on all @JS.Class@ classes. Calling @include()@ adds instance methods to the class, and @extend@
+  adds static methods, just like in Ruby. We could rewrite our @TodoItem@ class as:
+
+  <pre>
+  var TodoItem = new JS.Class({
+    initialize: function(position) {
+      this.position = position;
+    },
+
+    compareWith: function(other) {
+      if (this.position < other.position)
+        return -1;
+      else if (this.position > other.position)
+        return 1;
+      else
+        return 0;
+    }
+  });
+
+  TodoItem.include(Comparable);</pre>
+
+  @include@-ing/@extend@-ing a class like this will overwrite any existing methods with the same names
+  as those in the mixin, unless you pass @false@ as the second argument.
+
+  <pre>
+  TodoItem.include(Comparable, false);</pre>
+
+  If you @include()@ an object which itself has @include@ or @extend@ properties, these will be
+  treated as directives and applied to your class. So you can do this:
+
+  <pre>
+  var Enumerable = { /* methods... */ };
+
+  var Comparable = {
+    include: Enumerable,
+
+    /* methods... */
+  };
+
+  TodoItem.include(Comparable);
+
+  // TodoItem has instance methods from Enumerable and Comparable</pre>

site/src/pages/index.haml

@@ -6,7 +6,7 @@
 
   The first major release is now available. The download includes:
 
-  * @class.src.js@ - human-readable source code (8.14 kb)
+  * @class.src.js@ - human-readable source code (8.17 kb)
   * @class.js@ - a packed version (2.54 kb)
   * @class.js.gz@ - a gzipped version (1.29 kb)