diff --git a/lib/Grammar.php b/lib/Grammar.php
index 6d5e568..6af9875 100644
--- a/lib/Grammar.php
+++ b/lib/Grammar.php
@@ -8,9 +8,12 @@ namespace dW\Lit;
 use dW\Lit\Grammar\{
     BaseReference,
     CaptureList,
+    ChildGrammarRegistry,
     Exception,
+    FauxReadOnly,
     GrammarReference,
     InjectionList,
+    Node,
     Pattern,
     PatternList,
     Reference,
@@ -26,7 +29,6 @@ use dW\Lit\Grammar\{
  */
 class Grammar {
     use FauxReadOnly;
-
     protected ?string $_contentRegex;
     protected ?string $_firstLineMatch;
     protected ?InjectionList $_injections;
@@ -49,9 +51,12 @@ class Grammar {
         $this->_ownerGrammar = (is_null($ownerGrammar)) ? null : \WeakReference::create($ownerGrammar);
     }
 
+    // Used when adopting to change the $ownerGrammar property.
+    public function withOwnerGrammar(Grammar $ownerGrammar): self {
+        if ($new = ChildGrammarRegistry::get($this->_scopeName, $ownerGrammar)) {
+            return $new;
+        }
 
-    /** Clones the supplied grammar with this grammar set as its owner grammar */
-    public function adoptGrammar(self $grammar): self {
         $new = clone $this;
         if ($new->_patterns !== null) {
             $new->_patterns = $new->_patterns->withOwnerGrammar($new);
@@ -65,7 +70,10 @@ class Grammar {
             $new->_repository = $new->_repository->withOwnerGrammar($new);
         }
 
-        return GrammarRegistry::cacheChild($new);
+        $new->_ownerGrammar = \WeakReference::create($ownerGrammar);
+
+        ChildGrammarRegistry::set($this->_scopeName, $new);
+        return $new;
     }
 
 
@@ -147,7 +155,7 @@ class Grammar {
             } elseif ($pattern['include'] === '$base') {
                 return new BaseReference($this);
             } elseif ($pattern['include'] === '$self') {
-                return SelfReference::create($this);
+                return new SelfReference($this);
             } else {
                 return new GrammarReference($pattern['include'], $this);
             }
diff --git a/lib/Grammar/ChildGrammarRegistry.php b/lib/Grammar/ChildGrammarRegistry.php
new file mode 100644
index 0000000..13fb84e
--- /dev/null
+++ b/lib/Grammar/ChildGrammarRegistry.php
@@ -0,0 +1,61 @@
+<?php
+/** @license MIT
+ * Copyright 2021 Dustin Wilson et al.
+ * See LICENSE file for details */
+
+declare(strict_types=1);
+namespace dW\Lit\Grammar;
+use dW\Lit\Grammar;
+
+
+/**
+ * Static storage for child grammars; a map of a scope string and a Grammar
+ * object and checked against an owner grammar. Exists to prevent multiple clones
+ * of the same grammar from being created and also to give weak references a
+ * place in memory to access.
+ */
+class ChildGrammarRegistry {
+    protected static array $storage = [];
+
+    public static function clear(): bool {
+        self::$storage = [];
+        return true;
+    }
+
+    public static function get(string $scopeName, Grammar $ownerGrammar): ?Grammar {
+        if (!array_key_exists($scopeName, self::$storage)) {
+            return null;
+        }
+
+        $grammars = self::$storage[$scopeName];
+        foreach ($grammars as $g) {
+            if ($g->ownerGrammar === $ownerGrammar) {
+                return $g;
+            }
+        }
+
+        return null;
+    }
+
+    public static function set(string $scopeName, Grammar $grammar): bool {
+        try {
+            if (!array_key_exists($scopeName, self::$storage)) {
+                self::$storage[$scopeName] = [ $grammar ];
+                return true;
+            }
+
+            $grammars = self::$storage[$scopeName];
+            foreach ($grammars as $key => $value) {
+                if ($value->ownerGrammar === $grammar->ownerGrammar) {
+                    return false;
+                }
+            }
+
+            self::$storage[$scopeName][] = $grammar;
+        } catch (\Exception $e) {
+            return false;
+        }
+
+        return true;
+    }
+}
\ No newline at end of file
diff --git a/lib/Grammar/FauxReadOnly.php b/lib/Grammar/FauxReadOnly.php
new file mode 100644
index 0000000..af4a6fd
--- /dev/null
+++ b/lib/Grammar/FauxReadOnly.php
@@ -0,0 +1,26 @@
+<?php
+/** @license MIT
+ * Copyright 2021 Dustin Wilson et al.
+ * See LICENSE file for details */
+
+declare(strict_types=1);
+namespace dW\Lit\Grammar;
+
+
+trait FauxReadOnly {
+    public function __get(string $name) {
+        $prop = "_$name";
+        $exists = property_exists($this, $prop);
+        if ($name === 'ownerGrammar' && $exists) {
+            return $this->_ownerGrammar->get();
+        }
+
+        if (!$exists) {
+            $trace = debug_backtrace();
+            trigger_error("Cannot get undefined property $name in {$trace[0]['file']} on line {$trace[0]['line']}", E_USER_NOTICE);
+            return null;
+        }
+
+        return $this->$prop;
+    }
+}
\ No newline at end of file
diff --git a/lib/Grammar/GrammarReference.php b/lib/Grammar/GrammarReference.php
index 812ab21..8c1c512 100644
--- a/lib/Grammar/GrammarReference.php
+++ b/lib/Grammar/GrammarReference.php
@@ -36,7 +36,7 @@ class GrammarReference extends Reference {
             return null;
         }
 
-        $this->object = $this->_ownerGrammar->get()->adoptGrammar($grammar);
+        $this->object = $grammar->withOwnerGrammar($this->_ownerGrammar->get());
         return $this->object;
     }
 }
\ No newline at end of file
diff --git a/lib/Grammar/Pattern.php b/lib/Grammar/Pattern.php
index 89b2856..976b8d6 100644
--- a/lib/Grammar/Pattern.php
+++ b/lib/Grammar/Pattern.php
@@ -36,11 +36,4 @@ class Pattern extends Rule {
         $this->_applyEndPatternLast = $applyEndPatternLast;
         $this->_ownerGrammar = ($ownerGrammar === null) ? null : \WeakReference::create($ownerGrammar);
     }
-
-    // Used when adopting to change the $ownerGrammar property.
-    public function withOwnerGrammar(Grammar $ownerGrammar): self {
-        $new = clone $this;
-        $new->_ownerGrammar = \WeakReference::create($ownerGrammar);
-        return $new;
-    }
 }
\ No newline at end of file
diff --git a/lib/Grammar/Reference.php b/lib/Grammar/Reference.php
index 5949474..6005654 100644
--- a/lib/Grammar/Reference.php
+++ b/lib/Grammar/Reference.php
@@ -5,26 +5,7 @@
 
 declare(strict_types=1);
 namespace dW\Lit\Grammar;
-use dW\Lit\{
-    FauxReadOnly,
-    Grammar
-};
 
 
 /** Acts as a catch-all type for references */
-abstract class Reference extends Rule {
-    use FauxReadOnly;
-    protected \WeakReference $_ownerGrammar;
-
-
-    public function __construct(Grammar $ownerGrammar) {
-        $this->_ownerGrammar = \WeakReference::create($ownerGrammar);
-    }
-
-    // Used when adopting to change the $ownerGrammar property.
-    public function withOwnerGrammar(Grammar $ownerGrammar): self {
-        $new = clone $this;
-        $new->_ownerGrammar = \WeakReference::create($ownerGrammar);
-        return $new;
-    }
-}
\ No newline at end of file
+abstract class Reference extends Rule {}
\ No newline at end of file
diff --git a/lib/Grammar/RepositoryReference.php b/lib/Grammar/RepositoryReference.php
index b6d3dd1..b2f7112 100644
--- a/lib/Grammar/RepositoryReference.php
+++ b/lib/Grammar/RepositoryReference.php
@@ -30,10 +30,6 @@ class RepositoryReference extends Reference {
         }
 
         $grammar = $this->_ownerGrammar->get();
-        if (!isset($grammar->repository)) {
-            die(var_export($grammar));
-        }
-
         if (!isset($grammar->repository[$this->name])) {
             $this->object = false;
             return null;
diff --git a/lib/Grammar/Rule.php b/lib/Grammar/Rule.php
index 85324bd..a1abc0e 100644
--- a/lib/Grammar/Rule.php
+++ b/lib/Grammar/Rule.php
@@ -5,7 +5,7 @@
 
 declare(strict_types=1);
 namespace dW\Lit\Grammar;
-use dW\Lit\FauxReadOnly;
+use dW\Lit\Grammar;
 
 
 /**
@@ -13,4 +13,17 @@ use dW\Lit\FauxReadOnly;
  */
 abstract class Rule {
     use FauxReadOnly;
+    protected \WeakReference $_ownerGrammar;
+
+
+    public function __construct(Grammar $ownerGrammar) {
+        $this->_ownerGrammar = \WeakReference::create($ownerGrammar);
+    }
+
+    // Used when adopting to change the $ownerGrammar property.
+    public function withOwnerGrammar(Grammar $ownerGrammar): self {
+        $new = clone $this;
+        $new->_ownerGrammar = \WeakReference::create($ownerGrammar);
+        return $new;
+    }
 }
\ No newline at end of file
diff --git a/lib/Grammar/SelfReference.php b/lib/Grammar/SelfReference.php
index e794f14..6a877c1 100644
--- a/lib/Grammar/SelfReference.php
+++ b/lib/Grammar/SelfReference.php
@@ -12,21 +12,12 @@ use dW\Lit\Grammar;
  * exists to maintain sanity when checking types.
  */
 class SelfReference extends Reference {
-    protected ?Grammar $grammar;
-
-
-    public function __construct(Grammar $grammar, Grammar $ownerGrammar) {
-        $this->grammar = $grammar;
-        parent::__construct($ownerGrammar);
-    }
-
-    public function __destruct() {
-        parent::__destruct();
-        $this->grammar = null;
+    public function __construct(Grammar $grammar) {
+        parent::__construct($grammar);
     }
 
 
     public function get(): Grammar {
-        return $this->grammar;
+        return $this->_ownerGrammar->get();
     }
 }
\ No newline at end of file
diff --git a/lib/GrammarRegistry.php b/lib/GrammarRegistry.php
index 9cc32ee..76e286c 100644
--- a/lib/GrammarRegistry.php
+++ b/lib/GrammarRegistry.php
@@ -5,31 +5,17 @@
 
 declare(strict_types=1);
 namespace dW\Lit;
+use dW\Lit\Grammar\ChildGrammarRegistry;
 
 
 /** Static storage for grammars; a map of a scope string and a Grammar object */
-class GrammarRegistry implements \IteratorAggregate {
+class GrammarRegistry {
     protected static array $storage = [];
-    protected static array $childStorage = [];
-
-    public static function cacheChild(Grammar $grammar): Grammar {
-        self::$childStorage[] = $grammar;
-        return $grammar;
-    }
 
     public static function clear(): bool {
+        // Clear all the child grammars, too.
+        ChildGrammarRegistry::clear();
         self::$storage = [];
-        self::$childStorage = [];
-        return true;
-    }
-
-    public static function delete(string $scopeName): bool {
-        try {
-            unset(self::$storage[$scopeName]);
-        } catch (\Exception $e) {
-            return false;
-        }
-
         return true;
     }
 
@@ -48,22 +34,6 @@ class GrammarRegistry implements \IteratorAggregate {
         return false;
     }
 
-    public function getIterator(): \Traversable {
-        foreach (self::$storage as $scopeName => $grammar) {
-            yield $scopeName => $grammar;
-        }
-    }
-
-    public static function has(string $scopeName): bool {
-        return (array_key_exists($scopeName, self::$storage));
-    }
-
-    public static function keys(): \Traversable {
-        foreach (self::$storage as $scopeName => $_) {
-            yield $scopeName;
-        }
-    }
-
     public static function set(string $scopeName, Grammar $grammar): bool {
         try {
             self::$storage[$scopeName] = $grammar;
@@ -73,10 +43,4 @@ class GrammarRegistry implements \IteratorAggregate {
 
         return true;
     }
-
-    public function values(): \Traversable {
-        foreach (self::$storage as $grammar) {
-            yield $grammar;
-        }
-    }
 }
\ No newline at end of file
diff --git a/lib/Tokenizer.php b/lib/Tokenizer.php
index 2bc65eb..84e8680 100644
--- a/lib/Tokenizer.php
+++ b/lib/Tokenizer.php
@@ -63,6 +63,8 @@ class Tokenizer {
                                 'matches' => $match
                             ];
 
+                            die(var_export($rule));
+
                             if ($rule->begin !== null) {
                                 $this->ruleStack[] = $rule;
                                 $this->scopeStack[] = $scopeStack;