diff --git a/library/HTMLPurifier/AttrDef.php b/library/HTMLPurifier/AttrDef.php
index 754d995a..c1cdc7fa 100644
--- a/library/HTMLPurifier/AttrDef.php
+++ b/library/HTMLPurifier/AttrDef.php
@@ -5,7 +5,7 @@ class HTMLPurifier_AttrDef
 {
     function HTMLPurifier_AttrDef() {}
     
-    function validate() {
+    function validate($string, $config = null) {
         trigger_error('Cannot call abstract function', E_USER_ERROR);
     }
     
diff --git a/library/HTMLPurifier/AttrDef/Lang.php b/library/HTMLPurifier/AttrDef/Lang.php
new file mode 100644
index 00000000..a18b6b5c
--- /dev/null
+++ b/library/HTMLPurifier/AttrDef/Lang.php
@@ -0,0 +1,73 @@
+<?php
+
+require_once 'HTMLPurifier/AttrDef.php';
+
+// built according to RFC 3066, which obsoleted RFC 1766
+
+class HTMLPurifier_AttrDef_Lang extends HTMLPurifier_AttrDef
+{
+    
+    function validate($string) {
+        
+        $string = trim($string);
+        if (!$string) return false;
+        
+        $subtags = explode('-', $string);
+        $num_subtags = count($subtags);
+        
+        if ($num_subtags == 0) return false; // sanity check
+        
+        // process primary subtag : $subtags[0]
+        $length = strlen($subtags[0]);
+        switch ($length) {
+            case 0:
+                return false;
+            case 1:
+                if (! ($subtags[0] == 'x' || $subtags[0] == 'i') ) {
+                    return false;
+                }
+                break;
+            case 2:
+            case 3:
+                if (! ctype_alpha($subtags[0]) ) {
+                    return false;
+                } elseif (! ctype_lower($subtags[0]) ) {
+                    $subtags[0] = strtolower($subtags[0]);
+                }
+                break;
+            default:
+                return false;
+        }
+        
+        $new_string = $subtags[0];
+        if ($num_subtags == 1) return $new_string;
+        
+        // process second subtag : $subtags[1]
+        $length = strlen($subtags[1]);
+        if ($length == 0 || $length == 1 || $length > 8 || !ctype_alnum($subtags[1])) {
+            return $new_string;
+        }
+        if (!ctype_lower($subtags[1])) $subtags[1] = strotolower($subtags[1]);
+        
+        $new_string .= '-' . $subtags[1];
+        if ($num_subtags == 2) return $new_string;
+        
+        // process all other subtags, index 2 and up
+        for ($i = 2; $i < $num_subtags; $i++) {
+            $length = strlen($subtags[$i]);
+            if ($length == 0 || $length > 8 || !ctype_alnum($subtags[$i])) {
+                return $new_string;
+            }
+            if (!ctype_lower($subtags[$i])) {
+                $subtags[$i] = strotolower($subtags[$i]);
+            }
+            $new_string .= '-' . $subtags[$i];
+        }
+        
+        return $new_string;
+        
+    }
+    
+}
+
+?>
\ No newline at end of file
diff --git a/library/HTMLPurifier/AttrTransform.php b/library/HTMLPurifier/AttrTransform.php
new file mode 100644
index 00000000..8df5d3d2
--- /dev/null
+++ b/library/HTMLPurifier/AttrTransform.php
@@ -0,0 +1,14 @@
+<?php
+
+// AttrTransform = Attribute Transformation, when handling one attribute
+//                 isn't enough
+class HTMLPurifier_AttrTransform
+{
+    function HTMLPurifier_AttrTransform() {}
+    
+    function transform($token, $config = null) {
+        trigger_error('Cannot call abstract function', E_USER_ERROR);
+    }
+}
+
+?>
\ No newline at end of file
diff --git a/library/HTMLPurifier/AttrTransform/Lang.php b/library/HTMLPurifier/AttrTransform/Lang.php
new file mode 100644
index 00000000..fc0b72ba
--- /dev/null
+++ b/library/HTMLPurifier/AttrTransform/Lang.php
@@ -0,0 +1,31 @@
+<?php
+
+require_once 'HTMLPurifier/AttrTransform.php';
+
+class HTMLPurifier_AttrTransform_Lang extends HTMLPurifier_AttrTransform
+{
+    
+    function transform($token) {
+        
+        $lang     = isset($token->attributes['lang']) ?
+                          $token->attributes['lang'] : false;
+        $xml_lang = isset($token->attributes['xml:lang']) ?
+                          $token->attributes['xml:lang'] : false;
+        
+        if ($lang === false && $xml_lang == false) return $token;
+        
+        $new_token = $token->copy();
+        
+        if ($lang !== false && $xml_lang === false) {
+            $new_token->attributes['xml:lang'] = $lang;
+        } elseif ($xml_lang !== false) {
+            $new_token->attributes['lang'] = $xml_lang;
+        }
+        
+        return $new_token;
+        
+    }
+    
+}
+
+?>
\ No newline at end of file
diff --git a/library/HTMLPurifier/Definition.php b/library/HTMLPurifier/Definition.php
index 6af372ec..2ed84ab7 100644
--- a/library/HTMLPurifier/Definition.php
+++ b/library/HTMLPurifier/Definition.php
@@ -45,6 +45,9 @@ class HTMLPurifier_Definition
     // used solely by HTMLPurifier_Strategy_RemoveForeignElements
     var $info_tag_transform = array();
     
+    // used solely by HTMLPurifier_Strategy_ValidateAttributes
+    var $info_attr_transform = array();
+    
     // WARNING! Prototype is not passed by reference, so in order to get
     // a copy of the real one, you'll have to destroy your copy and
     // use instance() to get it.
@@ -238,11 +241,22 @@ class HTMLPurifier_Definition
         // which manually override these in their local definitions
         $this->info_global_attr = array(
             // core attrs
-            'id' => new HTMLPurifier_AttrDef_ID(),
+            'id'    => new HTMLPurifier_AttrDef_ID(),
             'class' => new HTMLPurifier_AttrDef_Class(),
             'title' => new HTMLPurifier_AttrDef_Text(),
             // i18n
-            'dir' => new HTMLPurifier_AttrDef_Enum(array('ltr','rtl'), false),
+            'dir'   => new HTMLPurifier_AttrDef_Enum(array('ltr','rtl'), false),
+            'lang'  => new HTMLPurifier_AttrDef_Lang(),
+            'xml:lang' => new HTMLPurifier_AttrDef_Lang(),
+            );
+        
+        // required attribute stipulation handled in attribute transformation
+        $this->info['bdo']->attr = array();
+        
+        $this->info['br']->attr = array(
+            'dir' => false,
+            'lang' => false,
+            'xml:lang' => false,
             );
         
         //////////////////////////////////////////////////////////////////////
@@ -275,9 +289,11 @@ class HTMLPurifier_Definition
         // UNIMP : info[]->attr_transform : attribute transformations in elements
         
         //////////////////////////////////////////////////////////////////////
-        // UNIMP : info_attr_transform : global attribute transform (for xml:lang)
+        // info_attr_transform : global attribute transformation that is
+        // unconditionally called. Good for transformations that have complex
+        // start conditions
         
-        // this might have bad implications for performance
+        $this->info_attr_transform[] = new HTMLPurifier_AttrTransform_Lang();
         
     }
     
diff --git a/library/HTMLPurifier/Strategy/ValidateAttributes.php b/library/HTMLPurifier/Strategy/ValidateAttributes.php
index fa382cc3..8793f802 100644
--- a/library/HTMLPurifier/Strategy/ValidateAttributes.php
+++ b/library/HTMLPurifier/Strategy/ValidateAttributes.php
@@ -26,11 +26,16 @@ class HTMLPurifier_Strategy_ValidateAttributes extends HTMLPurifier_Strategy
         $d_defs = $this->definition->info_global_attr;
         
         foreach ($tokens as $key => $token) {
-            if ($token->type !== 'start' && $token->type !== 'end') continue;
+            if ($token->type !== 'start' && $token->type !== 'empty') continue;
             
             // DEFINITION CALL
             $defs = $this->definition->info[$token->name]->attr;
             
+            // DEFINITION CALL
+            foreach ($this->definition->info_attr_transform as $transformer) {
+                $token = $transformer->transform($token);
+            }
+            
             $attr = $token->attributes;
             $changed = false;
             foreach ($attr as $attr_key => $value) {
diff --git a/library/HTMLPurifier/Token.php b/library/HTMLPurifier/Token.php
index 87e37f73..ed46621b 100644
--- a/library/HTMLPurifier/Token.php
+++ b/library/HTMLPurifier/Token.php
@@ -59,7 +59,9 @@ class HTMLPurifier_Token_Tag extends HTMLPurifier_Token // abstract
                 if (!isset($attributes[$new_key])) {
                     $attributes[$new_key] = $attributes[$key];
                 }
-                unset($attributes[$key]);
+                if ($new_key !== $key) {
+                    unset($attributes[$key]);
+                }
             }
         }
         $this->attributes = $attributes;
@@ -72,6 +74,9 @@ class HTMLPurifier_Token_Tag extends HTMLPurifier_Token // abstract
 class HTMLPurifier_Token_Start extends HTMLPurifier_Token_Tag
 {
     var $type = 'start';
+    function copy() {
+        return new HTMLPurifier_Token_Start($this->name, $this->attributes);
+    }
 }
 
 /**
@@ -80,6 +85,9 @@ class HTMLPurifier_Token_Start extends HTMLPurifier_Token_Tag
 class HTMLPurifier_Token_Empty extends HTMLPurifier_Token_Tag
 {
     var $type = 'empty';
+    function copy() {
+        return new HTMLPurifier_Token_Empty($this->name, $this->attributes);
+    }
 }
 
 /**
@@ -92,6 +100,9 @@ class HTMLPurifier_Token_Empty extends HTMLPurifier_Token_Tag
 class HTMLPurifier_Token_End extends HTMLPurifier_Token_Tag
 {
     var $type = 'end';
+    function copy() {
+        return new HTMLPurifier_Token_End($this->name);
+    }
 }
 
 /**
@@ -120,6 +131,9 @@ class HTMLPurifier_Token_Text extends HTMLPurifier_Token
         $this->data = $data;
         $this->is_whitespace = ctype_space($data);
     }
+    function copy() {
+        return new HTMLPurifier_Token_Text($this->data);
+    }
     
 }
 
@@ -138,6 +152,9 @@ class HTMLPurifier_Token_Comment extends HTMLPurifier_Token
     function HTMLPurifier_Token_Comment($data) {
         $this->data = $data;
     }
+    function copy() {
+        return new HTMLPurifier_Token_Comment($this->data);
+    }
 }
 
 ?>
\ No newline at end of file
diff --git a/tests/HTMLPurifier/AttrDef/LangTest.php b/tests/HTMLPurifier/AttrDef/LangTest.php
new file mode 100644
index 00000000..216a7a88
--- /dev/null
+++ b/tests/HTMLPurifier/AttrDef/LangTest.php
@@ -0,0 +1,83 @@
+<?php
+
+require_once 'HTMLPurifier/AttrDefHarness.php';
+require_once 'HTMLPurifier/AttrDef/Lang.php';
+
+class HTMLPurifier_AttrDef_LangTest extends HTMLPurifier_AttrDefHarness
+{
+    
+    function test() {
+        
+        $this->def = new HTMLPurifier_AttrDef_Lang();
+        
+        // basic good uses
+        $this->assertDef('en');
+        $this->assertDef('en-us');
+        
+        $this->assertDef(' en ', 'en'); // trim
+        $this->assertDef('EN', 'en'); // case insensitivity
+        
+        $this->assertDef('fr en', false); // multiple languages
+        $this->assertDef('%', false); // bad character
+        
+        // test overlong language according to syntax
+        $this->assertDef('thisistoolongsoitgetscut', false);
+        
+        // primary subtag rules
+            // I'm somewhat hesitant to allow x and i as primary language codes,
+            // because they usually are never used in real life. However,
+            // theoretically speaking, having them alone is permissble, so
+            // I'll be lenient. No XML parser is going to complain anyway.
+        $this->assertDef('x');
+        $this->assertDef('i');
+            // real world use-cases
+        $this->assertDef('x-klingon');
+        $this->assertDef('i-mingo');
+            // because the RFC only defines two and three letter primary codes,
+            // anything with a length of four or greater is invalid, despite
+            // the syntax stipulation of 1 to 8 characters. Because the RFC
+            // specifically states that this reservation is in order to allow
+            // for future versions to expand, the adoption of a new RFC will
+            // require these test cases to be rewritten, even if backwards-
+            // compatibility is largely retained (i.e. this is not forwards
+            // compatible)
+        $this->assertDef('four', false);
+            // for similar reasons, disallow any other one character language
+        $this->assertDef('f', false);
+        
+        // second subtag rules
+            // one letter subtags prohibited until revision. This is, however,
+            // less volatile than the restrictions on the primary subtags.
+            // Also note that this test-case tests fix-behavior: chop
+            // off subtags until you get a valid language code.
+        $this->assertDef('en-a', 'en');
+            // 2-8 chars are permitted, but have special meaning that cannot
+            // be checked without maintaining country code lookup tables (for
+            // two characters) or special registration tables (for all above).
+        $this->assertDef('en-uk', true);
+        
+        // further subtag rules: only syntactic constraints
+        $this->assertDef('en-us-edison');
+        $this->assertDef('en-us-toolonghaha', 'en-us');
+        $this->assertDef('en-us-a-silly-long-one');
+        
+        // rfc 3066 stipulates that if a three letter and a two letter code
+        // are available, the two letter one MUST be used. Without a language
+        // code lookup table, we cannot implement this functionality.
+        
+        // although the HTML protocol, technically speaking, allows you to
+        // omit language tags, this implicitly means that the parent element's
+        // language is the one applicable, which, in some cases, is incorrect.
+        // Thus, we allow und, only slightly defying the RFC's SHOULD NOT
+        // designation.
+        $this->assertDef('und');
+        
+        // because attributes only allow one language, mul is allowed, complying
+        // with the RFC's SHOULD NOT designation.
+        $this->assertDef('mul');
+        
+    }
+    
+}
+
+?>
\ No newline at end of file
diff --git a/tests/HTMLPurifier/AttrTransform/LangTest.php b/tests/HTMLPurifier/AttrTransform/LangTest.php
new file mode 100644
index 00000000..fa9273c9
--- /dev/null
+++ b/tests/HTMLPurifier/AttrTransform/LangTest.php
@@ -0,0 +1,60 @@
+<?php
+
+require_once 'HTMLPurifier/Token.php';
+require_once 'HTMLPurifier/AttrTransform/Lang.php';
+
+class HTMLPurifier_AttrTransform_LangTest extends UnitTestCase
+{
+    
+    function test() {
+        
+        $transform = new HTMLPurifier_AttrTransform_Lang();
+        
+        $inputs = array();
+        $expect = array();
+        
+        // leave non-lang'ed elements alone
+        $inputs[0] = new HTMLPurifier_Token_Start('b');
+        $expect[0] = $inputs[0];
+        
+        // copy lang to xml:lang
+        $inputs[1] = new HTMLPurifier_Token_Start('span',
+                        array('lang' => 'en'));
+        $expect[1] = new HTMLPurifier_Token_Start('span',
+                        array('lang' => 'en',
+                              'xml:lang' => 'en'));
+        
+        // empty tags must work too, also test attribute preservation
+        $inputs[2] = new HTMLPurifier_Token_Empty('img',
+                        array('src' => 'seine.png',
+                              'lang' => 'fr'));
+        $expect[2] = new HTMLPurifier_Token_Empty('img',
+                        array('src' => 'seine.png',
+                              'lang' => 'fr',
+                              'xml:lang' => 'fr'));
+        
+        // copy xml:lang to lang
+        $inputs[3] = new HTMLPurifier_Token_Start('span',
+                        array('xml:lang' => 'en'));
+        $expect[3] = new HTMLPurifier_Token_Start('span',
+                        array('lang' => 'en',
+                              'xml:lang' => 'en'));
+        
+        // both set, override lang with xml:lang
+        $inputs[4] = new HTMLPurifier_Token_Start('span',
+                        array('lang' => 'fr',
+                              'xml:lang' => 'de'));
+        $expect[4] = new HTMLPurifier_Token_Start('span',
+                        array('lang' => 'de',
+                              'xml:lang' => 'de'));
+        
+        foreach ($inputs as $i => $input) {
+            $result = $transform->transform($input);
+            $this->assertEqual($expect[$i], $result, "Test $i: %s");
+        }
+        
+    }
+    
+}
+
+?>
\ No newline at end of file
diff --git a/tests/HTMLPurifier/Strategy/ValidateAttributesTest.php b/tests/HTMLPurifier/Strategy/ValidateAttributesTest.php
index dbf7aea2..078cde7a 100644
--- a/tests/HTMLPurifier/Strategy/ValidateAttributesTest.php
+++ b/tests/HTMLPurifier/Strategy/ValidateAttributesTest.php
@@ -59,6 +59,10 @@ class HTMLPurifier_Strategy_ValidateAttributesTest extends
         $inputs[10] = '<acronym title="PHP: Hypertext Preprocessor">PHP</acronym>';
         $expect[10] = $inputs[10];
         
+        // test lang (NEEDS CORRECTION!)
+        $inputs[11] = '<span lang="fr">La soupe.</span>';
+        $expect[11] = '<span lang="fr" xml:lang="fr">La soupe.</span>';
+        
         $this->assertStrategyWorks($strategy, $inputs, $expect, $config);
         
     }
diff --git a/tests/index.php b/tests/index.php
index 190c3b91..5ff54b6c 100644
--- a/tests/index.php
+++ b/tests/index.php
@@ -42,8 +42,10 @@ $test->addTestFile('HTMLPurifier/AttrDef/EnumTest.php');
 $test->addTestFile('HTMLPurifier/AttrDef/IDTest.php');
 $test->addTestFile('HTMLPurifier/AttrDef/ClassTest.php');
 $test->addTestFile('HTMLPurifier/AttrDef/TextTest.php');
+$test->addTestFile('HTMLPurifier/AttrDef/LangTest.php');
 $test->addTestFile('HTMLPurifier/IDAccumulatorTest.php');
 $test->addTestFile('HTMLPurifier/TagTransformTest.php');
+$test->addTestFile('HTMLPurifier/AttrTransform/LangTest.php');
 
 if (SimpleReporter::inCli()) $reporter = new TextReporter();
 else $reporter = new HTMLReporter();