Implement attribute transforms for required attributes. I can now confidently say that output will always be valid.

git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@256 48356398-32a2-884e-a903-53898d9a118a

library/HTMLPurifier/AttrTransform/BdoDir.php

@@ -0,0 +1,25 @@
+<?php
+
+require_once 'HTMLPurifier/AttrTransform.php';
+
+// this MUST be placed in post, as it assumes that any value in dir is valid
+
+HTMLPurifier_ConfigDef::define(
+    'Attr', 'DefaultTextDir', 'ltr',
+    'Defines the default text direction (ltr or rtl) of the document '.
+    'being parsed.  This generally is the same as the value of the dir '.
+    'attribute in HTML, or ltr if that is not specified.'
+);
+
+class HTMLPurifier_AttrTransform_BdoDir extends HTMLPurifier_AttrTransform
+{
+    
+    function transform($attributes, $config) {
+        if (isset($attributes['dir'])) return $attributes;
+        $attributes['dir'] = $config->get('Attr', 'DefaultTextDir');
+        return $attributes;
+    }
+    
+}
+
+?>