diff --git a/library/HTMLPurifier/AttrContext.php b/library/HTMLPurifier/AttrContext.php
new file mode 100644
index 00000000..2dae4ad3
--- /dev/null
+++ b/library/HTMLPurifier/AttrContext.php
@@ -0,0 +1,15 @@
+<?php
+
+/**
+ * Internal data-structure used in attribute validation to accumulate state.
+ * 
+ * All it is is a data-structure that holds objects that accumulate state, like
+ * HTMLPurifier_IDAccumulator.
+ */
+
+class HTMLPurifier_AttrContext
+{
+    var $id_accumulator;
+}
+
+?>
\ No newline at end of file
diff --git a/library/HTMLPurifier/AttrDef.php b/library/HTMLPurifier/AttrDef.php
index c1cdc7fa..348c07fe 100644
--- a/library/HTMLPurifier/AttrDef.php
+++ b/library/HTMLPurifier/AttrDef.php
@@ -1,11 +1,13 @@
 <?php
 
+require_once 'HTMLPurifier/AttrContext.php';
+
 // AttrDef = Attribute Definition
 class HTMLPurifier_AttrDef
 {
     function HTMLPurifier_AttrDef() {}
     
-    function validate($string, $config = null) {
+    function validate($string, $config, &$context) {
         trigger_error('Cannot call abstract function', E_USER_ERROR);
     }
     
diff --git a/library/HTMLPurifier/AttrDef/Class.php b/library/HTMLPurifier/AttrDef/Class.php
index 2dec50dd..7e29f8ba 100644
--- a/library/HTMLPurifier/AttrDef/Class.php
+++ b/library/HTMLPurifier/AttrDef/Class.php
@@ -6,9 +6,7 @@ require_once 'HTMLPurifier/Config.php';
 class HTMLPurifier_AttrDef_Class extends HTMLPurifier_AttrDef
 {
     
-    function validate($string, $config = null) {
-        
-        if (!$config) $config = HTMLPurifier_Config::createDefault();
+    function validate($string, $config, &$context) {
         
         $string = trim($string);
         
diff --git a/library/HTMLPurifier/AttrDef/Enum.php b/library/HTMLPurifier/AttrDef/Enum.php
index be71c320..991cea21 100644
--- a/library/HTMLPurifier/AttrDef/Enum.php
+++ b/library/HTMLPurifier/AttrDef/Enum.php
@@ -14,7 +14,7 @@ class HTMLPurifier_AttrDef_Enum extends HTMLPurifier_AttrDef
         $this->case_sensitive = $case_sensitive;
     }
     
-    function validate($string, $config = null) {
+    function validate($string, $config, &$context) {
         $string = trim($string);
         if (!$this->case_sensitive) {
             $string = ctype_lower($string) ? $string : strtolower($string);
diff --git a/library/HTMLPurifier/AttrDef/ID.php b/library/HTMLPurifier/AttrDef/ID.php
index 1b33932a..6f110a34 100644
--- a/library/HTMLPurifier/AttrDef/ID.php
+++ b/library/HTMLPurifier/AttrDef/ID.php
@@ -12,12 +12,12 @@ require_once 'HTMLPurifier/IDAccumulator.php';
 class HTMLPurifier_AttrDef_ID extends HTMLPurifier_AttrDef
 {
     
-    function validate($id, $config, &$accumulator) {
+    function validate($id, $config, &$context) {
         
         $id = trim($id); // trim it first
         
         if ($id === '') return false;
-        if (isset($accumulator->ids[$id])) return false;
+        if (isset($context->id_accumulator->ids[$id])) return false;
         
         // we purposely avoid using regex, hopefully this is faster
         
@@ -32,7 +32,7 @@ class HTMLPurifier_AttrDef_ID extends HTMLPurifier_AttrDef
             $result = ($trim === '');
         }
         
-        if ($result) $accumulator->add($id);
+        if ($result) $context->id_accumulator->add($id);
         
         // if no change was made to the ID, return the result
         // else, return the new id if stripping whitespace made it
diff --git a/library/HTMLPurifier/AttrDef/Lang.php b/library/HTMLPurifier/AttrDef/Lang.php
index 61c639ea..3f82b730 100644
--- a/library/HTMLPurifier/AttrDef/Lang.php
+++ b/library/HTMLPurifier/AttrDef/Lang.php
@@ -7,7 +7,7 @@ require_once 'HTMLPurifier/AttrDef.php';
 class HTMLPurifier_AttrDef_Lang extends HTMLPurifier_AttrDef
 {
     
-    function validate($string, $config = null) {
+    function validate($string, $config, &$context) {
         
         $string = trim($string);
         if (!$string) return false;
diff --git a/library/HTMLPurifier/AttrDef/Length.php b/library/HTMLPurifier/AttrDef/Length.php
index 2bdf2d9d..6fb443a9 100644
--- a/library/HTMLPurifier/AttrDef/Length.php
+++ b/library/HTMLPurifier/AttrDef/Length.php
@@ -6,7 +6,7 @@ require_once 'HTMLPurifier/AttrDef/Pixels.php';
 class HTMLPurifier_AttrDef_Length extends HTMLPurifier_AttrDef_Pixels
 {
     
-    function validate($string, $config = null) {
+    function validate($string, $config, &$context) {
         
         $string = trim($string);
         if ($string === '') return false;
diff --git a/library/HTMLPurifier/AttrDef/MultiLength.php b/library/HTMLPurifier/AttrDef/MultiLength.php
index 583b52d3..c89ca198 100644
--- a/library/HTMLPurifier/AttrDef/MultiLength.php
+++ b/library/HTMLPurifier/AttrDef/MultiLength.php
@@ -6,7 +6,7 @@ require_once 'HTMLPurifier/AttrDef/Length.php';
 class HTMLPurifier_AttrDef_MultiLength extends HTMLPurifier_AttrDef_Length
 {
     
-    function validate($string, $config = null) {
+    function validate($string, $config, &$context) {
         
         $string = trim($string);
         if ($string === '') return false;
diff --git a/library/HTMLPurifier/AttrDef/NumberSpan.php b/library/HTMLPurifier/AttrDef/NumberSpan.php
index 9132eb02..acdfeb6b 100644
--- a/library/HTMLPurifier/AttrDef/NumberSpan.php
+++ b/library/HTMLPurifier/AttrDef/NumberSpan.php
@@ -6,7 +6,7 @@ require_once 'HTMLPurifier/AttrDef.php';
 class HTMLPurifier_AttrDef_NumberSpan extends HTMLPurifier_AttrDef
 {
     
-    function validate($string, $config = null) {
+    function validate($string, $config, &$context) {
         
         $string = trim($string);
         if ($string === '') return false;
diff --git a/library/HTMLPurifier/AttrDef/Pixels.php b/library/HTMLPurifier/AttrDef/Pixels.php
index 380d830f..652b4269 100644
--- a/library/HTMLPurifier/AttrDef/Pixels.php
+++ b/library/HTMLPurifier/AttrDef/Pixels.php
@@ -5,7 +5,7 @@ require_once 'HTMLPurifier/AttrDef.php';
 class HTMLPurifier_AttrDef_Pixels extends HTMLPurifier_AttrDef
 {
     
-    function validate($string, $config = null) {
+    function validate($string, $config, &$context) {
         
         $string = trim($string);
         if ($string === '0') return $string;
diff --git a/library/HTMLPurifier/AttrDef/Text.php b/library/HTMLPurifier/AttrDef/Text.php
index ed7e0be3..4a9850df 100644
--- a/library/HTMLPurifier/AttrDef/Text.php
+++ b/library/HTMLPurifier/AttrDef/Text.php
@@ -5,7 +5,7 @@ require_once 'HTMLPurifier/AttrDef.php';
 class HTMLPurifier_AttrDef_Text extends HTMLPurifier_AttrDef
 {
     
-    function validate($string, $config = null) {
+    function validate($string, $config, &$context) {
         return $this->parseCDATA($string);
     }
     
diff --git a/library/HTMLPurifier/AttrDef/URI.php b/library/HTMLPurifier/AttrDef/URI.php
index a315ebbd..1f5cd816 100644
--- a/library/HTMLPurifier/AttrDef/URI.php
+++ b/library/HTMLPurifier/AttrDef/URI.php
@@ -12,13 +12,11 @@ HTMLPurifier_ConfigDef::define(
 class HTMLPurifier_AttrDef_URI extends HTMLPurifier_AttrDef
 {
     
-    function validate($uri, $config = null) {
+    function validate($uri, $config, &$context) {
         
         // We'll write stack-based parsers later, for now, use regexps to
         // get things working as fast as possible (irony)
         
-        if (!$config) $config = HTMLPurifier_Config::createDefault();
-        
         // parse as CDATA
         $uri = $this->parseCDATA($uri);
         
diff --git a/library/HTMLPurifier/Strategy/ValidateAttributes.php b/library/HTMLPurifier/Strategy/ValidateAttributes.php
index af5b2c10..6c49780f 100644
--- a/library/HTMLPurifier/Strategy/ValidateAttributes.php
+++ b/library/HTMLPurifier/Strategy/ValidateAttributes.php
@@ -4,6 +4,7 @@ require_once 'HTMLPurifier/Strategy.php';
 require_once 'HTMLPurifier/Definition.php';
 require_once 'HTMLPurifier/IDAccumulator.php';
 require_once 'HTMLPurifier/ConfigDef.php';
+require_once 'HTMLPurifier/AttrContext.php';
 
 HTMLPurifier_ConfigDef::define(
     'Attr', 'IDBlacklist', array(),
@@ -27,11 +28,14 @@ class HTMLPurifier_Strategy_ValidateAttributes extends HTMLPurifier_Strategy
         // load default configuration object if none passed
         if (!$config) $config = HTMLPurifier_Config::createDefault();
         
+        // setup StrategyContext
+        $context = new HTMLPurifier_AttrContext();
+        
         // setup ID accumulator and load it with blacklisted IDs
         //     eventually, we'll have a dedicated context object to hold
         //     all these accumulators and caches. For now, just an IDAccumulator
-        $accumulator = new HTMLPurifier_IDAccumulator();
-        $accumulator->load($config->get('Attr', 'IDBlacklist'));
+        $context->id_accumulator = new HTMLPurifier_IDAccumulator();
+        $context->id_accumulator->load($config->get('Attr', 'IDBlacklist'));
         
         // create alias to global definition array, see also $defs
         // DEFINITION CALL
@@ -84,14 +88,14 @@ class HTMLPurifier_Strategy_ValidateAttributes extends HTMLPurifier_Strategy
                     } else {
                         // validate according to the element's definition
                         $result = $defs[$attr_key]->validate(
-                                        $value, $config, $accumulator
+                                        $value, $config, $context
                                    );
                     }
                 } elseif ( isset($d_defs[$attr_key]) ) {
                     // there is a global definition defined, validate according
                     // to the global definition
                     $result = $d_defs[$attr_key]->validate(
-                                    $value, $config, $accumulator
+                                    $value, $config, $context
                                );
                 } else {
                     // system never heard of the attribute? DELETE!
diff --git a/tests/HTMLPurifier/AttrDef/IDTest.php b/tests/HTMLPurifier/AttrDef/IDTest.php
index 4279ee02..4248102a 100644
--- a/tests/HTMLPurifier/AttrDef/IDTest.php
+++ b/tests/HTMLPurifier/AttrDef/IDTest.php
@@ -9,7 +9,8 @@ class HTMLPurifier_AttrDef_IDTest extends HTMLPurifier_AttrDefHarness
     
     function test() {
         
-        $this->id_accumulator = new HTMLPurifier_IDAccumulator();
+        $this->context = new HTMLPurifier_AttrContext();
+        $this->context->id_accumulator = new HTMLPurifier_IDAccumulator();
         $this->def = new HTMLPurifier_AttrDef_ID();
         
         // valid ID names
diff --git a/tests/HTMLPurifier/AttrDefHarness.php b/tests/HTMLPurifier/AttrDefHarness.php
index 79e4390f..98d0ef45 100644
--- a/tests/HTMLPurifier/AttrDefHarness.php
+++ b/tests/HTMLPurifier/AttrDefHarness.php
@@ -4,14 +4,15 @@ class HTMLPurifier_AttrDefHarness extends UnitTestCase
 {
     
     var $def;
-    var $id_accumulator;
+    var $context;
     var $config;
     
     // cannot be used for accumulator
     function assertDef($string, $expect = true) {
         // $expect can be a string or bool
         if (!$this->config) $this->config = HTMLPurifier_Config::createDefault();
-        $result = $this->def->validate($string, $this->config, $this->id_accumulator);
+        if (!$this->context) $this->context = new HTMLPurifier_AttrContext();
+        $result = $this->def->validate($string, $this->config, $this->context);
         if ($expect === true) {
             $this->assertIdentical($string, $result);
         } else {