diff --git a/src/alley/wp/class-registry.php b/src/alley/wp/class-registry.php
new file mode 100644
index 0000000..8acb1c5
--- /dev/null
+++ b/src/alley/wp/class-registry.php
@@ -0,0 +1,60 @@
+<?php
+/**
+ * Registry class file.
+ *
+ * @package wp-type-extensions
+ */
+
+namespace Alley\WP;
+
+/**
+ * Registry pattern class.
+ */
+final class Registry {
+	/**
+	 * Store all instances of every class.
+	 *
+	 * @var object[][]
+	 */
+	private static array $collection = [];
+
+	/**
+	 * Add a new instance to the collection.
+	 *
+	 * @param object $instance The class instance.
+	 * @return void
+	 */
+	public static function add( object $instance ): void {
+		if ( class_exists( $instance::class ) ) {
+			self::$collection[ $instance::class ] [] = $instance;
+		}
+	}
+
+	/**
+	 * Retrieve all instances of a class.
+	 *
+	 * @param string $class_name The class name.
+	 * @return object[]
+	 */
+	public static function get( string $class_name ): array {
+		if ( ! self::contains( $class_name ) ) {
+			return [];
+		}
+
+		return self::$collection[ $class_name ];
+	}
+
+	/**
+	 * Check if a class is registered in the collection.
+	 *
+	 * @param string $class_name The class name.
+	 * @return bool
+	 */
+	public static function contains( string $class_name ): bool {
+		if ( isset( self::$collection[ $class_name ] ) ) {
+			return true;
+		}
+
+		return false;
+	}
+}
diff --git a/src/alley/wp/post-ids/class-used-post-ids.php b/src/alley/wp/post-ids/class-used-post-ids.php
index 9f92187..66e3b6b 100644
--- a/src/alley/wp/post-ids/class-used-post-ids.php
+++ b/src/alley/wp/post-ids/class-used-post-ids.php
@@ -7,6 +7,7 @@
 
 namespace Alley\WP\Post_IDs;
 
+use Alley\WP\Registry;
 use Alley\WP\Types\Post_IDs;
 
 /**
@@ -27,7 +28,9 @@ final class Used_Post_IDs implements Post_IDs {
 	 */
 	public function __construct(
 		private readonly Post_IDs $seed = new Empty_Post_IDs()
-	) {}
+	) {
+		Registry::add( $this );
+	}
 
 	/**
 	 * Post IDs.
@@ -54,4 +57,13 @@ public function record( int|array $post_ids ): void {
 			}
 		}
 	}
+
+	/**
+	 * Clear recorded post IDs.
+	 *
+	 * @return void
+	 */
+	public function clear_recorded_post_ids(): void {
+		$this->ids = [];
+	}
 }