diff --git a/lib/Category/Collection.php b/lib/Category/Collection.php
index 0b0564c..a64a63b 100644
--- a/lib/Category/Collection.php
+++ b/lib/Category/Collection.php
@@ -7,13 +7,6 @@ declare(strict_types=1);
 namespace MensBeam\Lax\Category;
 
 class Collection extends \MensBeam\Lax\Collection {
-    protected static $ranks = [
-        'webmaster'   => 10,
-        'editor'      => 20,
-        'contributor' => 30,
-        'author'      => 40,
-    ];
-
     /** Returns the collection formatted as an array of strings
      *
      * The $humanFriendly parameter controls whether or not an effort is made to return human-friendly category names. Only Atom categories have this distinction
diff --git a/lib/Collection.php b/lib/Collection.php
index aa05c24..b4cb8b1 100644
--- a/lib/Collection.php
+++ b/lib/Collection.php
@@ -52,7 +52,7 @@ abstract class Collection implements \IteratorAggregate, \ArrayAccess, \Countabl
      *
      * The returned collection is the original instance, modified
      */
-    public function merge(Collection ...$coll): self {
+    public function merge(self ...$coll): self {
         foreach ($coll as $c) {
             foreach ($c as $p) {
                 $this[] = $p;
diff --git a/lib/Enclosure/Enclosure.php b/lib/Enclosure/Enclosure.php
index d3e8628..a12abae 100644
--- a/lib/Enclosure/Enclosure.php
+++ b/lib/Enclosure/Enclosure.php
@@ -6,14 +6,99 @@
 declare(strict_types=1);
 namespace MensBeam\Lax\Enclosure;
 
-class Enclosure {
-    public $url;
-    public $type;
-    public $title;
-    public $height;
-    public $width;
-    public $duration;
-    public $bitrate;
-    public $size;
+/**
+ * @property \MensBeam\Lax\Url $url
+ * @property string $type
+ * @property string $title
+ * @property int $height
+ * @property int $width
+ * @property int $duration
+ * @property int $bitrate
+ * @property int $size
+ * @property bool $preferred
+ */
+class Enclosure implements \IteratorAggregate, \ArrayAccess, \Countable {
     public $preferred;
+    protected $data = [];
+    private $url;
+    private $type;
+    private $title;
+    private $height;
+    private $width;
+    private $duration;
+    private $bitrate;
+    private $size;
+
+    public function __construct(Enclosure ...$enc) {
+        $this->data = $enc ?? [];
+    }
+
+    public function getIterator(): \Traversable {
+        return new \ArrayIterator($this->data);
+    }
+
+    public function count(): int {
+        return count($this->data);
+    }
+
+    public function offsetExists($offset): bool {
+        return isset($this->data[$offset]);
+    }
+
+    public function offsetGet($offset) {
+        return $this->data[$offset];
+    }
+
+    public function offsetSet($offset, $value): void {
+        if (is_null($offset)) {
+            $this->data[] = $value;
+        } else {
+            $this->data[$offset] = $value;
+        }
+    }
+
+    public function offsetUnset($offset): void {
+        unset($this->data[$offset]);
+    }
+
+    public function __set(string $name, $value): void {
+        if ($this->data) {
+            $this->default()->__set($name, $value);
+        } else {
+            $this->$name = $value;
+        }
+    }
+
+    public function __get(string $name) {
+        if ($this->data) {
+            return $this->default()->__get($name);
+        } else {
+            return $this->$name;
+        }
+    }
+
+    public function __isset(string $name): bool {
+        if ($this->data) {
+            return $this->default()->__isset($name);
+        } else {
+            return isset($this->$name);
+        }
+    }
+
+    public function __unset(string $name): void {
+        if ($this->data) {
+            $this->default()->__unset($name);
+        } else {
+            unset($this->$name);
+        }
+    }
+
+    protected function default(): self {
+        foreach ($this->data as $m) {
+            if ($m->preferred) {
+                return $m;
+            }
+        }
+        return $this->data[array_keys($this->data)[0]];
+    }
 }
diff --git a/tests/cases/Util/EnclosureTest.php b/tests/cases/Util/EnclosureTest.php
new file mode 100644
index 0000000..a12d9c3
--- /dev/null
+++ b/tests/cases/Util/EnclosureTest.php
@@ -0,0 +1,96 @@
+<?php
+/** @license MIT
+ * Copyright 2018 J. King
+ * See LICENSE and AUTHORS files for details */
+
+declare(strict_types=1);
+namespace MensBeam\Lax\TestCase\Util;
+
+use MensBeam\Lax\Enclosure\Enclosure;
+use MensBeam\Lax\Url;
+
+/** @covers \MensBeam\Lax\Enclosure\Enclosure */
+class EnclosureTest extends \PHPUnit\Framework\TestCase {
+    public function testCreateAnEnclosure(): void {
+        $url = new Url("http://example.com");
+        $enc = new Enclosure;
+        $enc->preferred = true;
+        $enc->url = $url;
+        $this->assertTrue($enc->preferred);
+        $this->assertSame($url, $enc->url);
+    }
+
+    public function testCreateAnEnclosureSet(): void {
+        // create an empty enclosure
+        $enc = new Enclosure;
+        $this->assertSame(0, count($enc));
+        $this->assertFalse(isset($enc->title));
+        // create two more enclosures; the second is preferred
+        $enc1 = new Enclosure;
+        $enc1->title = "Ook";
+        $enc2 = new Enclosure;
+        $enc2->title = "Eek";
+        $enc2->preferred = true;
+        // add the first sub-enclosure
+        $enc[] = $enc1;
+        $this->assertTrue(isset($enc->title));
+        $this->assertSame(1, count($enc));
+        $this->assertSame("Ook", $enc->title);
+        // add the second sub-enclosure
+        $enc[] = $enc2;
+        $this->assertSame(2, count($enc));
+        $this->assertSame("Eek", $enc->title);
+        // make the second enclosure non-preferred
+        $enc2->preferred = false;
+        $this->assertSame("Ook", $enc->title);
+    }
+
+    public function testIterateOverAnEnclosureSet(): void {
+        // create four enclosures
+        $enc1 = new Enclosure;
+        $enc2 = new Enclosure;
+        $enc3 = new Enclosure;
+        $enc4 = new Enclosure;
+        // create a set with two of the enclosures
+        $enc = new Enclosure($enc1, $enc2);
+        // add the other two with arbitrary keys
+        $enc['ook'] = $enc3;
+        $enc[] = $enc4;
+        // iterate over the sub-enclosures
+        $act = [];
+        foreach ($enc as $k => $v) {
+            $act[$k] = $v;
+        }
+        $exp = [0 => $enc1, 1 => $enc2, 'ook' => $enc3, 2 => $enc4];
+        $this->assertSame($exp, $act);
+    }
+
+    public function testManipulateMagicEnclosureProperties(): void {
+        // create two enclosures
+        $enc1 = new Enclosure;
+        $enc2 = new Enclosure;
+        $enc1->title = "Ook";
+        $enc2->title = "Eek";
+        // create a set with the two enclosures
+        $enc = new Enclosure($enc1, $enc2);
+        // check titles
+        $this->assertTrue(isset($enc[0]));
+        $this->assertTrue(isset($enc[1]));
+        $this->assertSame("Ook", $enc[0]->title);
+        $this->assertSame("Eek", $enc[1]->title);
+        $this->assertSame("Ook", $enc->title);
+        // unset the title of the first sub-enclosure via the parent
+        unset($enc->title);
+        $this->assertFalse(isset($enc[0]->title));
+        $this->assertFalse(isset($enc->title));
+        // remove the first sub-enclosure
+        unset($enc[0]);
+        $this->assertFalse(isset($enc[0]));
+        $this->assertTrue(isset($enc[1]));
+        $this->assertSame("Eek", $enc->title);
+        // set the title of the second enclosure via the parent
+        $enc->title = "Ack";
+        $this->assertSame("Ack", $enc[1]->title);
+        $this->assertSame("Ack", $enc->title);
+    }
+}