MDL-9151 HTML Purifier cleaning support - enable switch is in experimental section

MDL-9435 Reviewved url cleaning in redirect()

lib/htmlpurifier/HTMLPurifier/AttrTransform.php

@@ -0,0 +1,34 @@
+<?php
+
+/**
+ * Processes an entire attribute array for corrections needing multiple values.
+ * 
+ * Occasionally, a certain attribute will need to be removed and popped onto
+ * another value.  Instead of creating a complex return syntax for
+ * HTMLPurifier_AttrDef, we just pass the whole attribute array to a
+ * specialized object and have that do the special work.  That is the
+ * family of HTMLPurifier_AttrTransform.
+ * 
+ * An attribute transformation can be assigned to run before or after
+ * HTMLPurifier_AttrDef validation.  See HTMLPurifier_HTMLDefinition for
+ * more details.
+ */
+
+class HTMLPurifier_AttrTransform
+{
+    
+    /**
+     * Abstract: makes changes to the attributes dependent on multiple values.
+     * 
+     * @param $attr Assoc array of attributes, usually from
+     *              HTMLPurifier_Token_Tag::$attr
+     * @param $config Mandatory HTMLPurifier_Config object.
+     * @param $context Mandatory HTMLPurifier_Context object
+     * @returns Processed attribute array.
+     */
+    function transform($attr, $config, &$context) {
+        trigger_error('Cannot call abstract function', E_USER_ERROR);
+    }
+}
+
+?>