diff --git a/library/HTMLPurifier.includes.php b/library/HTMLPurifier.includes.php
index e637c4ac..ae75fc3b 100644
--- a/library/HTMLPurifier.includes.php
+++ b/library/HTMLPurifier.includes.php
@@ -130,6 +130,8 @@ require 'HTMLPurifier/ConfigDef/Namespace.php';
 require 'HTMLPurifier/ConfigSchema/Exception.php';
 require 'HTMLPurifier/ConfigSchema/Interchange.php';
 require 'HTMLPurifier/ConfigSchema/InterchangeBuilder.php';
+require 'HTMLPurifier/ConfigSchema/Validator.php';
+require 'HTMLPurifier/ConfigSchema/ValidatorAtom.php';
 require 'HTMLPurifier/ConfigSchema/Builder/ConfigSchema.php';
 require 'HTMLPurifier/ConfigSchema/Interchange/Directive.php';
 require 'HTMLPurifier/ConfigSchema/Interchange/Id.php';
diff --git a/library/HTMLPurifier/ConfigSchema/Interchange.php b/library/HTMLPurifier/ConfigSchema/Interchange.php
index 4390b480..1b1a2489 100644
--- a/library/HTMLPurifier/ConfigSchema/Interchange.php
+++ b/library/HTMLPurifier/ConfigSchema/Interchange.php
@@ -11,12 +11,12 @@ class HTMLPurifier_ConfigSchema_Interchange
     /**
      * Array of Namespace ID => array(namespace info)
      */
-    public $namespaces;
+    public $namespaces = array();
     
     /**
      * Array of Directive ID => array(directive info)
      */
-    public $directives;
+    public $directives = array();
     
     /**
      * Adds a namespace array to $namespaces
@@ -29,7 +29,7 @@ class HTMLPurifier_ConfigSchema_Interchange
      * Adds a directive array to $directives
      */
     public function addDirective($directive) {
-        $this->directives[(string) $directive->id] = $directive;
+        $this->directives[$directive->id->__toString()] = $directive;
     }
     
 }
diff --git a/library/HTMLPurifier/ConfigSchema/Validator.php b/library/HTMLPurifier/ConfigSchema/Validator.php
new file mode 100644
index 00000000..ff10a93a
--- /dev/null
+++ b/library/HTMLPurifier/ConfigSchema/Validator.php
@@ -0,0 +1,51 @@
+<?php
+
+/**
+ * Performs validations on HTMLPurifier_ConfigSchema_Interchange
+ */
+class HTMLPurifier_ConfigSchema_Validator
+{
+    
+    protected $interchange;
+    
+    /**
+     * Volatile context variables to provide a fluent interface.
+     */
+    protected $context, $obj, $member;
+    
+    /**
+     * Validates a fully-formed interchange object. Throws an
+     * HTMLPurifier_ConfigSchema_Exception if there's a problem.
+     */
+    public function validate($interchange) {
+        $this->interchange = $interchange;
+        foreach ($interchange->namespaces as $namespace) {
+            $this->validateNamespace($namespace);
+        }
+        foreach ($interchange->directives as $directive) {
+            $this->validateDirective($directive);
+        }
+    }
+    
+    public function validateNamespace($n) {
+        $this->context = "namespace '{$n->namespace}'";
+        $this->with($n, 'namespace')
+            ->assertIsString()
+            ->assertNotEmpty()
+            ->assertAlnum();
+        $this->with($n, 'description')
+            ->assertIsString()
+            ->assertNotEmpty();
+    }
+    
+    public function validateDirective($d) {
+        $this->context = "directive '{$d->id}'";
+    }
+    
+    // protected helper functions
+    
+    protected function with($obj, $member) {
+        return new HTMLPurifier_ConfigSchema_ValidatorAtom($this->interchange, $this->context, $obj, $member);
+    }
+    
+}
diff --git a/library/HTMLPurifier/ConfigSchema/ValidatorAtom.php b/library/HTMLPurifier/ConfigSchema/ValidatorAtom.php
new file mode 100644
index 00000000..0ebacf80
--- /dev/null
+++ b/library/HTMLPurifier/ConfigSchema/ValidatorAtom.php
@@ -0,0 +1,47 @@
+<?php
+
+/**
+ * Fluent interface for validating the contents of member variables.
+ * This should be immutable. See HTMLPurifier_ConfigSchema_Validator for
+ * use-cases.
+ */
+class HTMLPurifier_ConfigSchema_ValidatorAtom
+{
+    
+    protected $interchange, $context, $obj, $member, $contents;
+    
+    public function __construct($interchange, $context, $obj, $member) {
+        $this->interchange = $interchange;
+        $this->context     = $context;
+        $this->obj         = $obj;
+        $this->member      = $member;
+        $this->contents    =& $obj->$member;
+    }
+    
+    public function assertIsString() {
+        if (!is_string($this->contents)) $this->error('must be a string');
+        return $this;
+    }
+    
+    public function assertNotNull() {
+        if (is_null($this->contents)) $this->error('must not be null');
+        return $this;
+    }
+    
+    public function assertAlnum() {
+        if (!ctype_alnum($this->contents)) $this->error('must be alphanumeric');
+        return $this;
+    }
+    
+    public function assertNotEmpty() {
+        if (empty($this->contents)) $this->error('must not be empty');
+        return $this;
+    }
+    
+    protected function error($msg) {
+        throw new HTMLPurifier_ConfigSchema_Exception('Member variable \'' . $this->member . '\' in ' . $this->context . ' ' . $msg);
+    }
+    
+}
+
+
diff --git a/maintenance/generate-schema-cache.php b/maintenance/generate-schema-cache.php
index 4b693ee5..a61615c9 100644
--- a/maintenance/generate-schema-cache.php
+++ b/maintenance/generate-schema-cache.php
@@ -24,6 +24,9 @@ foreach ($files as $file) {
     $builder->build($interchange, new HTMLPurifier_StringHash($parser->parseFile($file)));
 }
 
+$validator = new HTMLPurifier_ConfigSchema_Validator();
+$validator->validate($interchange);
+
 $schema_builder = new HTMLPurifier_ConfigSchema_Builder_ConfigSchema();
 $schema = $schema_builder->build($interchange);
 
diff --git a/tests/HTMLPurifier/ConfigSchema/ValidatorTest.php b/tests/HTMLPurifier/ConfigSchema/ValidatorTest.php
new file mode 100644
index 00000000..1bb5246d
--- /dev/null
+++ b/tests/HTMLPurifier/ConfigSchema/ValidatorTest.php
@@ -0,0 +1,69 @@
+<?php
+
+class HTMLPurifier_ConfigSchema_ValidatorTest extends UnitTestCase
+{
+    
+    protected $interchange, $validator;
+    
+    public function setup() {
+        $this->interchange = new HTMLPurifier_ConfigSchema_Interchange();
+        $this->validator   = new HTMLPurifier_ConfigSchema_Validator();
+    }
+    
+    /**
+     * Adds a namespace to our interchange object.
+     */
+    protected function addNamespace($namespace, $description) {
+        $obj = new HTMLPurifier_ConfigSchema_Interchange_Namespace();
+        $obj->namespace   = $namespace;
+        $obj->description = $description;
+        $this->interchange->addNamespace($obj);
+    }
+    
+    /**
+     * Invokes a validation, so we can fish for exceptions
+     */
+    protected function validate() {
+        $this->validator->validate($this->interchange);
+    }
+    
+    protected function expectValidationException($msg) {
+        $this->expectException(new HTMLPurifier_ConfigSchema_Exception($msg));
+    }
+    
+    public function testNamespace() {
+        $this->addNamespace('Namespace', 'This is a generic namespace');
+        $this->validate();
+    }
+    
+    public function testNamespaceNamespaceString() {
+        $this->addNamespace(3, 'Description');
+        $this->expectValidationException("Member variable 'namespace' in namespace '3' must be a string");
+        $this->validate();
+    }
+    
+    public function testNamespaceNamespaceNotEmpty() {
+        $this->addNamespace('0', 'Description');
+        $this->expectValidationException("Member variable 'namespace' in namespace '0' must not be empty");
+        $this->validate();
+    }
+    
+    public function testNamespaceNamespaceAlnum() {
+        $this->addNamespace('%', 'Description');
+        $this->expectValidationException("Member variable 'namespace' in namespace '%' must be alphanumeric");
+        $this->validate();
+    }
+    
+    public function testNamespaceDescriptionString() {
+        $this->addNamespace('Ns', 3);
+        $this->expectValidationException("Member variable 'description' in namespace 'Ns' must be a string");
+        $this->validate();
+    }
+    
+    public function testNamespaceDescriptionNotEmpty() {
+        $this->addNamespace('Ns', '');
+        $this->expectValidationException("Member variable 'description' in namespace 'Ns' must not be empty");
+        $this->validate();
+    }
+    
+}