Implement HTML.Nofollow for external links.

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>

library/HTMLPurifier/HTMLModule/Nofollow.php

@@ -0,0 +1,19 @@
+<?php
+
+/**
+ * Module adds the nofollow attribute transformation to a tags.  It
+ * is enabled by HTML.Nofollow
+ */
+class HTMLPurifier_HTMLModule_Nofollow extends HTMLPurifier_HTMLModule
+{
+
+    public $name = 'Nofollow';
+
+    public function setup($config) {
+        $a = $this->addBlankElement('a');
+        $a->attr_transform_post[] = new HTMLPurifier_AttrTransform_Nofollow();
+    }
+
+}
+
+// vim: et sw=4 sts=4