diff --git a/core/core.services.yml b/core/core.services.yml
index d915e10..1167f20 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -559,3 +559,7 @@ services:
     tags:
       - { name: event_subscriber }
     arguments: ['@authentication']
+  asset.library_repository:
+    class: Drupal\Core\Asset\AssetLibraryRepository
+    arguments: ['@module_handler']
+
diff --git a/core/lib/Drupal/Core/Asset/AssetBag.php b/core/lib/Drupal/Core/Asset/AssetBag.php
new file mode 100644
index 0000000..6beec9d
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/AssetBag.php
@@ -0,0 +1,150 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Asset\AssetBag.
+ */
+
+namespace Drupal\Core\Asset;
+
+use Drupal\Core\Asset\AssetInterface;
+use Drupal\Core\Asset\AssetBagInterface;
+
+/**
+ * The default AssetBag, used to declare assets needed for a response.
+ */
+class AssetBag implements AssetBagInterface {
+
+  /**
+   * The assets in this AssetBag.
+   *
+   * @var array
+   */
+  protected $assets = array();
+
+  /**
+   * Whether this AssetBag contains any JavaScript assets.
+   *
+   * @var bool
+   */
+  protected $hasJs = FALSE;
+
+  /**
+   * Whether this AssetBag contains any CSS assets.
+   *
+   * @var bool
+   */
+  protected $hasCss = FALSE;
+
+  /**
+   * Whether this AssetBag is frozen.
+   *
+   * @var bool
+   */
+  protected $frozen = FALSE;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function add(AssetInterface $asset) {
+    if ($this->isFrozen()) {
+      throw new \LogicException('Assets cannot be added to a frozen AssetBag.', E_ERROR);
+    }
+
+    $this->assets[] = $asset;
+    if ($asset instanceof JavascriptAssetInterface) {
+      $this->hasJs = TRUE;
+    }
+    if ($asset instanceof StylesheetAssetInterface) {
+      $this->hasCss = TRUE;
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function addAssetBag(AssetBagInterface $bag, $freeze = TRUE) {
+    if ($this->isFrozen()) {
+      throw new \LogicException('Assets cannot be added to a frozen AssetBag.', E_ERROR);
+    }
+
+    foreach ($bag->all() as $asset) {
+      $this->add($asset);
+    }
+
+    if ($freeze) {
+      $bag->freeze();
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function hasCss() {
+    return $this->hasCss;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCss() {
+    $css = array();
+    foreach ($this->assets as $asset) {
+      if ($asset instanceof StylesheetAssetInterface) {
+        $css[] = $asset;
+      }
+    }
+
+    return $css;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function all() {
+    return $this->assets;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function addJsSetting($data) {
+    $this->javascript['settings']['data'][] = $data;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function hasJs() {
+    return $this->hasJs;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getJs() {
+    $js = array();
+    foreach ($this->assets as $asset) {
+      if ($asset instanceof JavascriptAssetInterface) {
+        $js[] = $asset;
+      }
+    }
+
+    return $js;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function freeze() {
+    $this->frozen = TRUE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isFrozen() {
+    return $this->frozen;
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Asset/AssetBagInterface.php b/core/lib/Drupal/Core/Asset/AssetBagInterface.php
new file mode 100644
index 0000000..b32ada4
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/AssetBagInterface.php
@@ -0,0 +1,111 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Asset\AssetBagInterface.
+ */
+
+namespace Drupal\Core\Asset;
+
+use Drupal\Core\Asset\AssetInterface;
+use Symfony\Component\DependencyInjection\ContainerAwareInterface;
+
+/**
+ * Defines a common interface for asset bags.
+ *
+ * Asset bags are a mechanism for internal Drupal code to list a set of assets
+ * and provide some metadata about their manner of use. During a normal page
+ * build, a number of these bags are likely to be built and ultimately merged
+ * onto the Response object.
+ *
+ * An AssetBagInterface object's contents are not expected to be in the final,
+ * ordered form in which it will ultimately be delivered as part of the page
+ * response. Rather, a stack of such bags will be combined towards the end of
+ * the page request into the final asset list.
+ */
+interface AssetBagInterface {
+
+  /**
+   * Adds another Asset to this AssetBag.
+   *
+   * @param AssetInterface $asset
+   *
+   * @return mixed
+   */
+  public function add(AssetInterface $asset);
+
+  /**
+   * Adds another AssetBag to this one.
+   *
+   * @param AssetBagInterface $bag
+   *
+   * @return mixed
+   */
+  public function addAssetBag(AssetBagInterface $bag);
+
+  /**
+   * Adds configuration settings for eventual inclusion in drupalSettings.
+   *
+   * @todo Nice-to-have: create something like JavaScriptSettingAssetInterface.
+   *
+   * @param $data
+   *   An associative array containing configuration settings, to be eventually
+   *   merged into drupalSettings. Settings should be be keyed, typically by
+   *   by module name, in order to avoid conflicts in the drupalSettings object.
+   *   Calling this twice with the same data does not change the settings sent
+   *   to the browser: this is idempotent, thanks to drupal_merge_js_settings().
+   *
+   * @return AssetBagInterface $this
+   *   Returns the current AssetBagInterface object for method chaining.
+   */
+  public function addJsSetting($data);
+
+  /**
+   * Indicates whether this object contains any CSS assets.
+   *
+   * @return bool
+   */
+  public function hasCss();
+
+  /**
+   * Returns the CSS assets in this bag, in the order they were added.
+   *
+   * @return array
+   */
+  public function getCss();
+
+  /**
+   * Indicates whether this AssetBagInterface contains any JavaScript assets.
+   *
+   * @return bool
+   */
+  public function hasJs();
+
+  /**
+   * Returns the JavaScript assets in this bag, in the order they were added.
+   *
+   * @return array
+   */
+  public function getJs();
+
+  /**
+   * Returns all assets contained in this object, in the order they were added.
+   *
+   * @return array
+   */
+  public function all();
+
+  /**
+   * Marks this bag as incapable of receiving new data.
+   *
+   * @return void
+   */
+  public function freeze();
+
+  /**
+   * Indicates whether or not this bag is frozen.
+   *
+   * @return bool
+   */
+  public function isFrozen();
+}
diff --git a/core/lib/Drupal/Core/Asset/AssetCollector.php b/core/lib/Drupal/Core/Asset/AssetCollector.php
new file mode 100644
index 0000000..c338482
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/AssetCollector.php
@@ -0,0 +1,207 @@
+<?php
+/**
+ * @file
+ * Contains Drupal\Core\Asset\AssetCollector.
+ */
+
+namespace Drupal\Core\Asset;
+
+/**
+ * A class that helps to create and collect assets.
+ *
+ * This class should be set with appropriate defaults, injected with an AssetBag
+ * for collection, then injected into an asset-producing segment of code in
+ * order to ease the creation and collection of asset information.
+ */
+class AssetCollector {
+
+  /**
+   * The bag used to store any assets that are added.
+   *
+   * @var \Drupal\Core\Asset\AssetBagInterface
+   */
+  protected $bag;
+
+  /**
+   * Flag indicating whether or not the object is locked.
+   *
+   * Locking prevents modifying the underlying defaults or the current bag.
+   *
+   * @var bool
+   */
+  protected $locked = FALSE;
+
+  /**
+   * The key with which the lock was set.
+   *
+   * This exact value (===) must be provided in order to unlock the instance.
+   *
+   * There are no type restrictions.
+   *
+   * @var mixed
+   */
+  protected $lockKey;
+
+  protected $defaultAssetDefaults = array(
+    'css' => array(
+      'group' => CSS_AGGREGATE_DEFAULT,
+      'weight' => 0,
+      'every_page' => FALSE,
+      'media' => 'all',
+      'preprocess' => TRUE,
+      'browsers' => array(
+        'IE' => TRUE,
+        '!IE' => TRUE,
+      ),
+    ),
+    'js' => array(
+      'group' => JS_DEFAULT,
+      'every_page' => FALSE,
+      'weight' => 0,
+      'scope' => 'header',
+      'cache' => TRUE,
+      'preprocess' => TRUE,
+      'attributes' => array(),
+      'version' => NULL,
+      'browsers' => array(),
+    ),
+  );
+
+  protected $assetDefaults = array();
+
+  protected $classMap = array(
+    'css' => array(
+      'file' => 'Drupal\\Core\\Asset\\StylesheetFileAsset',
+      'external' => 'Drupal\\Core\\Asset\\StylesheetExternalAsset',
+      'string' => 'Drupal\\Core\\Asset\\StylesheetStringAsset',
+    ),
+    'js' => array(
+      'file' => 'Drupal\\Core\\Asset\\JavascriptFileAsset',
+      'external' => 'Drupal\\Core\\Asset\\JavascriptExternalAsset',
+      'string' => 'Drupal\\Core\\Asset\\JavascriptStringAsset',
+     ),
+  );
+
+  public function __construct() {
+    $this->restoreDefaults();
+  }
+
+  /**
+   * Adds an asset to the injected AM
+   *
+   * @todo Document.
+   */
+  public function add(AssetInterface $asset) {
+    if (empty($this->bag)) {
+      throw new \Exception('No bag is currently attached to this collector.');
+    }
+    $this->bag->add($asset);
+    return $this;
+  }
+
+  /**
+   * Creates an asset and returns it.
+   *
+   * @param string $asset_type
+   *   'css' or 'js'.
+   * @param string $source_type
+   *   'file', 'external' or 'string'.
+   * @param ??? $data
+   * @param array $options
+   *   ???
+   * @param array $filters
+   *   ???
+   *
+   * @return \Drupal\Core\Asset\AssetInterface
+   */
+  public function create($asset_type, $source_type, $data, $options = array(), $filters = array()) {
+    if (!isset($this->classMap[$asset_type])) {
+      throw new \InvalidArgumentException('Only assets of type "js" or "css" are allowed.');
+    }
+    if (!isset($this->classMap[$asset_type][$source_type])) {
+      throw new \InvalidArgumentException('Only sources of type "file", "string", or "external" are allowed.');
+    }
+
+    $class = $this->classMap[$asset_type][$source_type];
+    $asset = new $class($data, $options, $filters);
+    $asset->setDefaults($this->getDefaults($asset_type));
+
+    if (!empty($this->bag)) {
+      $this->add($asset);
+    }
+
+    return $asset;
+  }
+
+  public function setBag(AssetBagInterface $bag) {
+    if ($this->isLocked()) {
+      throw new \Exception('The collector instance is locked. A new bag cannot assigned on a locked collector.');
+    }
+    $this->bag = $bag;
+  }
+
+  public function clearBag() {
+    if ($this->isLocked()) {
+      throw new \Exception('The collector instance is locked. Bags cannot be cleared on a locked collector.');
+    }
+    $this->bag = NULL;
+  }
+
+  public function createJavascriptSetting() {
+    // TODO figure out settings
+  }
+
+  public function lock($key) {
+    if ($this->isLocked()) {
+      throw new \Exception('Collector is already locked.', E_WARNING);
+    }
+
+    $this->locked = TRUE;
+    $this->lockKey = $key;
+    return TRUE;
+  }
+
+  public function unlock($key) {
+    if (!$this->isLocked()) {
+      throw new \Exception('Collector is not locked', E_WARNING);
+    }
+
+    if ($this->lockKey !== $key) {
+      throw new \Exception('Attempted to unlock Collector with incorrect key.', E_WARNING);
+    }
+
+    $this->locked = FALSE;
+    $this->lockKey = NULL;
+    return TRUE;
+  }
+
+  public function isLocked() {
+    return $this->locked;
+  }
+
+  public function setDefaults($type, array $defaults) {
+    if ($this->isLocked()) {
+      throw new \Exception('The collector instance is locked. Asset defaults cannot be modified on a locked collector.');
+    }
+    $this->assetDefaults[$type] = array_merge($this->assetDefaults[$type], $defaults);
+  }
+
+  public function getDefaults($type = NULL) {
+    if (!isset($type)) {
+      return $this->assetDefaults;
+    }
+
+    if (!isset($this->assetDefaults[$type])) {
+      throw new \InvalidArgumentException(sprintf('The type provided, "%s", is not known.', $type));
+    }
+
+    return $this->assetDefaults[$type];
+  }
+
+  public function restoreDefaults() {
+    if ($this->isLocked()) {
+      throw new \Exception('The collector instance is locked. Asset defaults cannot be modified on a locked collector.');
+    }
+    $this->assetDefaults = $this->defaultAssetDefaults;
+  }
+}
diff --git a/core/lib/Drupal/Core/Asset/AssetDependencyInterface.php b/core/lib/Drupal/Core/Asset/AssetDependencyInterface.php
new file mode 100644
index 0000000..bf37208
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/AssetDependencyInterface.php
@@ -0,0 +1,52 @@
+<?php
+/**
+ * @file
+ * Contains Drupal\Core\Asset\AssetDependencyInterface.
+ */
+
+namespace Drupal\Core\Asset;
+
+/**
+ * Describes an asset or asset-like object that can declare dependencies.
+ */
+interface AssetDependencyInterface {
+
+  /**
+   * Indicates whether this asset has one or more dependencies.
+   *
+   * @return boolean
+   */
+  public function hasDependencies();
+
+  /**
+   * Retrieve this asset's dependencies.
+   *
+   * @return ???
+   *
+   * @todo Document.
+   */
+  public function getDependencies();
+
+  /**
+   * Add a dependency for this asset.
+   *
+   * @param string $module
+   *   A module name.
+   * @param string $name
+   *   ???
+   *
+   * @return ???
+   *
+   * @todo Document.
+   */
+  public function addDependency($module, $name);
+
+  /**
+   * Clears (removes) all dependencies for this asset.
+   *
+   * @return ???
+   *
+   * @todo Document.
+   */
+  public function clearDependencies();
+}
diff --git a/core/lib/Drupal/Core/Asset/AssetInterface.php b/core/lib/Drupal/Core/Asset/AssetInterface.php
new file mode 100644
index 0000000..5d7f306
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/AssetInterface.php
@@ -0,0 +1,55 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Asset\AssetInterface.
+ */
+
+namespace Drupal\Core\Asset;
+
+use Assetic\Asset\AssetInterface as AsseticAssetInterface;
+
+/**
+ * Represents an asset.
+ *
+ * This interface extends the AssetInterface provided by Assetic to allow
+ * more sophisticated logic and behaviors to be attached to individual assets.
+ */
+interface AssetInterface extends AsseticAssetInterface, AssetDependencyInterface, \ArrayAccess {
+
+  /**
+   * Indicates whether or not this asset is eligible for preprocessing.
+   *
+   * Assets that are marked as not preprocessable will always be passed directly
+   * to the browser without aggregation or minification. Assets that are marked
+   * as eligible for preprocessing will be included in any broader aggregation
+   * logic that has been configured.
+   *
+   * @return bool
+   */
+  public function isPreprocessable();
+
+  /**
+   * Sets default metadata to be used for this asset.
+   *
+   * @param array $defaults
+   *   An associative array of default values for the common metadata properties
+   *   associated with Drupal assets, such as 'browser', 'preprocess', etc. The
+   *   specific values vary by asset type.
+   *
+   * @return void
+   */
+  public function setDefaults(array $defaults);
+
+  /**
+   * Indicates whether the value at the key is explicitly set, or a default.
+   *
+   * @param $key
+   *   The key to check.
+   *
+   * @return bool
+   *   TRUE if the value is served by a default, FALSE if it was explicitly set.
+   */
+  public function isDefault($key);
+
+}
diff --git a/core/lib/Drupal/Core/Asset/AssetLibrary.php b/core/lib/Drupal/Core/Asset/AssetLibrary.php
new file mode 100644
index 0000000..d264fd4a
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/AssetLibrary.php
@@ -0,0 +1,163 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Asset\AssetLibrary.
+ */
+
+namespace Drupal\Core\Asset;
+
+use Drupal\Core\Asset\AssetBag;
+
+class AssetLibrary extends AssetBag implements AssetDependencyInterface {
+
+  /**
+   * The asset library's title.
+   *
+   * @var string
+   */
+  protected $title = '';
+
+  /**
+   * The asset library's version.
+   *
+   * @var string
+   */
+  protected $version;
+
+  /**
+   * The asset library's website.
+   *
+   * @var string
+   */
+  protected $website = '';
+
+  /**
+   * The asset library's dependencies (on other asset libraries).
+   *
+   * @var array
+   */
+  protected $dependencies = array();
+
+  public function __construct(array $values = array()) {
+    // TODO do it right.
+    $vals = array_intersect_key($values, array_flip(array('title', 'version', 'website', 'dependencies')));
+    foreach ($vals as $key => $val) {
+      $this->$key = $val;
+    }
+  }
+
+  /**
+   * Set the asset library's title.
+   *
+   * @param string $title
+   *   The title of the asset library.
+   *
+   * @return \Drupal\Core\Asset\AssetLibrary
+   *   The asset library, to allow for chaining.
+   */
+  public function setTitle($title) {
+    $this->attemptWrite();
+    $this->title = $title;
+    return $this;
+  }
+
+  /**
+   * Get the asset library's title.
+   *
+   * @return string
+   *   The title of the asset library.
+   */
+  public function getTitle() {
+    return $this->title;
+  }
+
+  /**
+   * Set the asset library's website.
+   *
+   * @param string $website
+   *   The website of the asset library.
+   *
+   * @return \Drupal\Core\Asset\AssetLibrary
+   *   The asset library, to allow for chaining.
+   */
+  public function setWebsite($website) {
+    $this->attemptWrite();
+    $this->website = $website;
+    return $this;
+  }
+
+  /**
+   * Get the asset library's website.
+   *
+   * @return string
+   *   The website of the asset library.
+   */
+  public function getWebsite() {
+    return $this->website;
+  }
+
+  /**
+   * Set the asset library's version.
+   *
+   * @param string $version
+   *   The version of the asset library.
+   *
+   * @return \Drupal\Core\Asset\AssetLibrary
+   *   The asset library, to allow for chaining.
+   */
+  public function setVersion($version) {
+    $this->attemptWrite();
+    $this->version = $version;
+    return $this;
+  }
+
+  /**
+   * Get the asset library's version.
+   *
+   * @return string
+   *   The version of the asset library.
+   */
+  public function getVersion() {
+    return $this->version;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function hasDependencies() {
+    return !empty($this->dependencies);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function addDependency($module, $name) {
+    $this->attemptWrite();
+    $this->dependencies[] = array($module, $name);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function clearDependencies() {
+    $this->attemptWrite();
+    $this->dependencies = array();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDependencies() {
+    return $this->dependencies;
+  }
+
+  /**
+   * Checks if the asset library is frozen, throws an exception if it is.
+   */
+  protected function attemptWrite() {
+    if ($this->isFrozen()) {
+      throw new \LogicException('Metadata cannot be modified on a frozen AssetLibrary.');
+    }
+  }
+}
diff --git a/core/lib/Drupal/Core/Asset/AssetLibraryCollector.php b/core/lib/Drupal/Core/Asset/AssetLibraryCollector.php
new file mode 100644
index 0000000..b1239cd
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/AssetLibraryCollector.php
@@ -0,0 +1,95 @@
+<?php
+/**
+ * @file
+ * Contains Drupal\Core\Asset\AssetLibraryCollector.
+ */
+
+namespace Drupal\Core\Asset;
+
+use Drupal\Component\Utility\Crypt;
+use \Drupal\Core\Asset\AssetLibraryRepository;
+use \Drupal\Core\Asset\AssetCollector;
+
+class AssetLibraryCollector {
+
+  /**
+   * @var \Drupal\Core\Asset\AssetLibraryRepository
+   */
+  protected $manager;
+
+  protected $module;
+
+  protected $locked;
+
+  protected $lockKey;
+
+  protected $privateKey;
+
+  public function __construct(AssetLibraryRepository $manager) {
+    $this->manager = $manager;
+  }
+
+  public function add($name, AssetLibrary $library) {
+    $this->manager->add($this->module, $name, $library);
+    return $this;
+  }
+
+  public function buildLibrary($name, $values) {
+    $library = $this->createLibrary($name, $values);
+
+    $collector = new AssetCollector();
+    $collector->setBag($library);
+    $collector->setDefaults('js', array('group' => JS_LIBRARY));
+    $collector->lock($this->getPrivateKey()); // TODO is locking here a bad idea?
+
+    return $collector;
+  }
+
+  public function createLibrary($name, $values) {
+    $library = new AssetLibrary($values);
+    $this->add($name, $library);
+
+    return $library;
+  }
+
+  public function setModule($module) {
+    $this->module = $module;
+  }
+
+  public function lock($key) {
+    if ($this->isLocked()) {
+      throw new \Exception('Collector is already locked.', E_WARNING);
+    }
+
+    $this->locked = TRUE;
+    $this->lockKey = $key;
+    return TRUE;
+  }
+
+  public function unlock($key) {
+    if (!$this->isLocked()) {
+      throw new \Exception('Collector is not locked', E_WARNING);
+    }
+
+    if ($this->lockKey !== $key) {
+      throw new \Exception('Attempted to unlock Collector with incorrect key.', E_WARNING);
+    }
+
+    $this->locked = FALSE;
+    $this->lockKey = NULL;
+    return TRUE;
+  }
+
+  public function isLocked() {
+    return $this->locked;
+  }
+
+  protected function getPrivateKey() {
+    if (empty($this->privateKey)) {
+      // This doesn't need to be highly secure, just decently random.
+      $this->privateKey = Crypt::randomStringHashed(8);
+    }
+    return $this->privateKey;
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Asset/AssetLibraryRepository.php b/core/lib/Drupal/Core/Asset/AssetLibraryRepository.php
new file mode 100644
index 0000000..55108fc
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/AssetLibraryRepository.php
@@ -0,0 +1,157 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Asset\AssetLibraryRepository.
+ */
+
+namespace Drupal\Core\Asset;
+
+use Drupal\Core\Asset\AssetLibrary;
+use Drupal\Core\Extension\ModuleHandlerInterface;
+
+/**
+ * @todo Transform this into a 'lazy' library - serialize & load as needed.
+ */
+class AssetLibraryRepository implements \IteratorAggregate {
+
+  protected $libraries;
+
+  protected $flattened;
+
+  /**
+   * Indicates whether or not the repository has initialized its collection.
+   *
+   * @todo this is very dirty; shift responsibility for populating to something external
+   *
+   * @var bool
+   */
+  protected $initialized = FALSE;
+
+  /**
+   * The module handler.
+   *
+   * @var \Drupal\Core\Extension\ModuleHandlerInterface
+   */
+  protected $moduleHandler;
+
+  function __construct($module_handler) {
+    $this->moduleHandler = $module_handler;
+  }
+
+  protected function initialize() {
+    if ($this->initialized) {
+      return;
+    }
+    $this->initialized = TRUE;
+
+    $library_collector = new AssetLibraryCollector($this);
+    foreach ($this->moduleHandler->getImplementations('library_info') as $module) {
+      $library_collector->setModule($module);
+      $libraries = call_user_func("{$module}_library_info");
+      foreach ($libraries as $name => $info) {
+        // Normalize - apparently hook_library_info is allowed to be sloppy.
+        $info += array('dependencies' => array(), 'js' => array(), 'css' => array());
+
+        // @todo This works sorta sanely because of the array_intersect_key() hack in AssetLibrary::construct()
+        $asset_collector = $library_collector->buildLibrary($name, $info);
+        foreach (array('js', 'css') as $type) {
+          if (!empty($info[$type])) {
+            foreach ($info[$type] as $data => $options) {
+              if (is_scalar($options)) {
+                $data = $options;
+                $options = array();
+              }
+              // @todo good enough for now to assume these are all file assets
+              $asset_collector->create($type, 'file', $data, $options);
+            }
+          }
+        }
+      }
+    }
+  }
+
+  /**
+   * Gets a library by composite key.
+   *
+   * @param string $module
+   *   The module owner that declared the library.
+   *
+   * @param string $name
+   *   The library name.
+   *
+   * @return \Drupal\Core\Asset\AssetLibrary
+   *   The requested library.
+   *
+   * @throws \InvalidArgumentException If there is no library by that name
+   */
+  public function get($module, $name) {
+    $this->initialize();
+    if (!isset($this->libraries[$module][$name])) {
+      throw new \InvalidArgumentException(sprintf('There is library identified by "%s/%s" in the manager.', $module, $name));
+    }
+
+    return $this->libraries[$module][$name];
+  }
+
+  /**
+   * Checks if the current library manager has a certain library.
+   *
+   * @param string $module
+   *   The module owner that declared the library.
+   *
+   * @param string $name
+   *   The library name.
+   *
+   * @return bool
+   *   True if the library has been set, false if not
+   */
+  public function has($module, $name) {
+    $this->initialize();
+    return isset($this->libraries[$module][$name]);
+  }
+
+  public function add($module, $name, AssetLibrary $library) {
+    // TODO add validation - alphanum + underscore only
+    if (!isset($this->libraries[$module])) {
+      $this->libraries[$module] = array();
+    }
+
+    $this->libraries[$module][$name] = $library;
+    $this->flattened = NULL;
+  }
+
+  /**
+   * Returns an array of library names.
+   *
+   * @return array An array of library names
+   */
+  public function getNames() {
+    $this->initialize();
+    return array_keys($this->libraries);
+  }
+
+  /**
+   * Clears all libraries.
+   */
+  public function clear() {
+    $this->initialize();
+    $this->libraries = array();
+    $this->flattened = NULL;
+  }
+
+  public function getIterator() {
+    $this->initialize();
+    if (is_null($this->flattened)) {
+      $this->flattened = array();
+      foreach ($this->libraries as $module => $set) {
+        foreach ($set as $name => $library) {
+          $this->flattened["$module:$name"] = $library;
+        }
+      }
+    }
+
+    return new \ArrayIterator($this->flattened);
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Asset/BaseAsset.php b/core/lib/Drupal/Core/Asset/BaseAsset.php
new file mode 100644
index 0000000..e2316df
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/BaseAsset.php
@@ -0,0 +1,284 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Asset\BaseAsset.
+ */
+
+namespace Drupal\Core\Asset;
+
+use Assetic\Filter\FilterCollection;
+use Assetic\Filter\FilterInterface;
+use Drupal\Core\Asset\AssetInterface;
+
+/**
+ * A base abstract asset.
+ *
+ * This is an amalgam of Assetic\Asset\BaseAsset (copied directly) with
+ * implementations of the additional methods specified by Drupal's own
+ * Drupal\Core\Asset\AssetInterface.
+ *
+ * The methods load() and getLastModified() are left undefined, although a
+ * reusable doLoad() method is available to child classes.
+ */
+abstract class BaseAsset implements AssetInterface {
+
+  protected $filters;
+
+  protected $sourceRoot;
+
+  protected $sourcePath;
+
+  protected $targetPath;
+
+  protected $content;
+
+  protected $loaded;
+
+  protected $vars;
+
+  protected $values;
+
+  protected $metadata;
+
+  protected $metadataDefaults;
+
+  protected $dependencies;
+
+  public function __construct(array $options = array(), $filters = array(), $sourceRoot = NULL, $sourcePath = NULL) {
+    $this->filters = new FilterCollection($filters);
+    $this->sourceRoot = $sourceRoot;
+    $this->sourcePath = $sourcePath;
+    $this->vars = array(); // TODO remove
+    $this->values = array(); // TODO remove
+    $this->loaded = FALSE;
+
+    foreach ($options as $k => $v) {
+      $this->metadata[$k] = $v;
+    }
+  }
+
+  public function __clone() {
+    $this->filters = clone $this->filters;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function ensureFilter(FilterInterface $filter) {
+    $this->filters->ensure($filter);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFilters() {
+    return $this->filters->all();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function clearFilters() {
+    $this->filters->clear();
+  }
+
+  /**
+   * Encapsulates asset loading logic.
+   *
+   * @param string          $content          The asset content
+   * @param FilterInterface $additionalFilter An additional filter
+   */
+  protected function doLoad($content, FilterInterface $additionalFilter = NULL) {
+    $filter = clone $this->filters;
+    if ($additionalFilter) {
+      $filter->ensure($additionalFilter);
+    }
+
+    $asset = clone $this;
+    $asset->setContent($content);
+
+    $filter->filterLoad($asset);
+    $this->content = $asset->getContent();
+
+    $this->loaded = TRUE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function dump(FilterInterface $additionalFilter = NULL) {
+    if (!$this->loaded) {
+      $this->load();
+    }
+
+    $filter = clone $this->filters;
+    if ($additionalFilter) {
+      $filter->ensure($additionalFilter);
+    }
+
+    $asset = clone $this;
+    $filter->filterDump($asset);
+
+    return $asset->getContent();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getContent() {
+    return $this->content;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setContent($content) {
+    $this->content = $content;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getSourceRoot() {
+    return $this->sourceRoot;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getSourcePath() {
+    return $this->sourcePath;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getTargetPath() {
+    return $this->targetPath;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setTargetPath($targetPath) {
+    if ($this->vars) {
+      foreach ($this->vars as $var) {
+        if (FALSE === strpos($targetPath, $var)) {
+          throw new \RuntimeException(sprintf('The asset target path "%s" must contain the variable "{%s}".', $targetPath, $var));
+        }
+      }
+    }
+
+    $this->targetPath = $targetPath;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getVars() {
+    // TODO turn this off
+    return $this->vars;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setValues(array $values) {
+    // TODO turn this off
+    foreach ($values as $var => $v) {
+      if (!in_array($var, $this->vars, TRUE)) {
+        throw new \InvalidArgumentException(sprintf('The asset with source path "%s" has no variable named "%s".', $this->sourcePath, $var));
+      }
+    }
+
+    $this->values = $values;
+    $this->loaded = FALSE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getValues() {
+    return $this->values;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isPreprocessable() {
+    return (bool) $this->metadata['preprocess'];
+  }
+
+  public function setDefaults(array $defaults) {
+    $this->metadataDefaults = $defaults;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isDefault($offset) {
+    if (!$this->offsetExists($offset)) {
+      return;
+    }
+
+    return !isset($this->metadata);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function offsetExists($offset) {
+    return isset($this->metadata) || isset($this->metadataDefaults);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function offsetGet($offset) {
+    return $this->metadata[$offset] ?: $this->metadataDefaults[$offset];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function offsetSet($offset, $value) {
+    $this->metadata[$offset] = $value;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function offsetUnset($offset) {
+    // TODO probably a gotcha that this only unsets the explicit val, but still better than breaking pattern around how defaults work
+    unset($this->metadata[$offset]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function hasDependencies() {
+    return !empty($this->dependencies);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function addDependency($module, $name) {
+    $this->dependencies[] = array($module, $name);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function clearDependencies() {
+    $this->dependencies = array();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDependencies() {
+    return $this->dependencies;
+  }
+}
diff --git a/core/lib/Drupal/Core/Asset/BaseExternalAsset.php b/core/lib/Drupal/Core/Asset/BaseExternalAsset.php
new file mode 100644
index 0000000..abe6834
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/BaseExternalAsset.php
@@ -0,0 +1,74 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Asset\BaseFileAsset.
+ */
+
+namespace Drupal\Core\Asset;
+
+use Assetic\Util\PathUtils;
+use Assetic\Filter\FilterInterface;
+use Drupal\Core\Asset\BaseAsset;
+
+abstract class BaseExternalAsset extends BaseAsset {
+
+  protected $sourceUrl;
+
+  public function __construct($sourceUrl, $options = array(), $filters = array()) {
+    if (0 === strpos($sourceUrl, '//')) {
+      $sourceUrl = 'http:' . $sourceUrl;
+    }
+    elseif (FALSE === strpos($sourceUrl, '://')) {
+      throw new \InvalidArgumentException(sprintf('"%s" is not a valid URL.', $sourceUrl));
+    }
+
+    $this->sourceUrl = $sourceUrl;
+    $this->ignoreErrors = FALSE; // TODO expose somehow
+
+    list($scheme, $url) = explode('://', $sourceUrl, 2);
+    list($host, $path) = explode('/', $url, 2);
+
+    parent::__construct($options, $filters, $scheme.'://'.$host, $path);
+  }
+  /**
+   * Returns the time the current asset was last modified.
+   *
+   * @todo copied right from Assetic. needs to be made more Drupalish.
+   *
+   * @return integer|null A UNIX timestamp
+   */
+  public function getLastModified() {
+    if (false !== @file_get_contents($this->sourceUrl, false, stream_context_create(array('http' => array('method' => 'HEAD'))))) {
+      foreach ($http_response_header as $header) {
+        if (0 === stripos($header, 'Last-Modified: ')) {
+          list(, $mtime) = explode(':', $header, 2);
+
+          return strtotime(trim($mtime));
+        }
+      }
+    }
+  }
+
+  /**
+   * Loads the asset into memory and applies load filters.
+   *
+   * You may provide an additional filter to apply during load.
+   *
+   * @param FilterInterface $additionalFilter An additional filter
+   */
+  public function load(FilterInterface $additionalFilter = NULL) {
+    // TODO convert PathUtils call
+    if (false === $content = @file_get_contents(PathUtils::resolvePath(
+      $this->sourceUrl, $this->getVars(), $this->getValues()))) {
+      if ($this->ignoreErrors) {
+        return;
+      } else {
+        throw new \RuntimeException(sprintf('Unable to load asset from URL "%s"', $this->sourceUrl));
+      }
+    }
+
+    $this->doLoad($content, $additionalFilter);
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Asset/BaseFileAsset.php b/core/lib/Drupal/Core/Asset/BaseFileAsset.php
new file mode 100644
index 0000000..415532a
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/BaseFileAsset.php
@@ -0,0 +1,56 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Asset\BaseFileAsset.
+ */
+
+namespace Drupal\Core\Asset;
+
+use Assetic\Util\PathUtils;
+use Assetic\Filter\FilterInterface;
+use Drupal\Core\Asset\BaseAsset;
+
+abstract class BaseFileAsset extends BaseAsset {
+
+  protected $source;
+
+  public function __construct($source, array $options = array(), $filters = array()) {
+    $sourceRoot = dirname($source);
+    $sourcePath = basename($source);
+    $this->source = $source;
+
+    parent::__construct($options, $filters, $sourceRoot, $sourcePath);
+  }
+
+  /**
+   * Returns the time the current asset was last modified.
+   *
+   * @return integer|null A UNIX timestamp
+   */
+  public function getLastModified() {
+    if (!is_file($this->source)) {
+      throw new \RuntimeException(sprintf('The source file "%s" does not exist.', $this->source));
+    }
+
+    return filemtime($this->source);
+  }
+
+  /**
+   * Loads the asset into memory and applies load filters.
+   *
+   * You may provide an additional filter to apply during load.
+   *
+   * @todo copied right from Assetic. needs to be made more Drupalish.
+   *
+   * @param FilterInterface $additionalFilter An additional filter
+   */
+  public function load(FilterInterface $additionalFilter = NULL) {
+    if (!is_file($this->source)) {
+      throw new \RuntimeException(sprintf('The source file "%s" does not exist.', $this->source));
+    }
+
+    $this->doLoad(file_get_contents($this->source), $additionalFilter);
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Asset/BaseStringAsset.php b/core/lib/Drupal/Core/Asset/BaseStringAsset.php
new file mode 100644
index 0000000..e51a3ef
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/BaseStringAsset.php
@@ -0,0 +1,35 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Asset\BaseInlineAsset.
+ */
+
+namespace Drupal\Core\Asset;
+
+use Assetic\Filter\FilterInterface;
+use Drupal\Core\Asset\BaseAsset;
+
+abstract class BaseStringAsset extends BaseAsset {
+
+  protected $lastModified;
+
+  public function __construct($content, $options = array(), $filters = array()) {
+    $this->content = $content;
+    $this->lastModified = REQUEST_TIME;
+
+    parent::__construct($options, $filters);
+  }
+
+  public function setLastModified($last_modified) {
+    $this->lastModified = $last_modified;
+  }
+
+  public function getLastModified() {
+    return $this->lastModified;
+  }
+
+  public function load(FilterInterface $additionalFilter = NULL) {
+    $this->doLoad($this->content, $additionalFilter);
+  }
+}
diff --git a/core/lib/Drupal/Core/Asset/JavascriptAssetInterface.php b/core/lib/Drupal/Core/Asset/JavascriptAssetInterface.php
new file mode 100644
index 0000000..01f4930
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/JavascriptAssetInterface.php
@@ -0,0 +1,28 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Asset\JavascriptAssetInterface.
+ */
+
+namespace Drupal\Core\Asset;
+
+use Drupal\Core\Asset\AssetInterface;
+
+/**
+ * Represents a JavaScript asset.
+ */
+interface JavascriptAssetInterface extends AssetInterface {
+
+  public function setScope($scope);
+
+  public function getScope();
+
+  public function getScopeDefault();
+
+//  public function addDependency($name);
+//
+//  public function hasDependencies();
+//
+//  public function getDependencies();
+}
diff --git a/core/lib/Drupal/Core/Asset/JavascriptExternalAsset.php b/core/lib/Drupal/Core/Asset/JavascriptExternalAsset.php
new file mode 100644
index 0000000..0984dd7
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/JavascriptExternalAsset.php
@@ -0,0 +1,38 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Asset\JavascriptExternalAsset.
+ */
+
+namespace Drupal\Core\Asset;
+
+use Drupal\Core\Asset\JavascriptAssetInterface;
+use Drupal\Core\Asset\BaseExternalAsset;
+
+class JavascriptExternalAsset extends BaseExternalAsset implements JavascriptAssetInterface {
+
+  protected $scope;
+
+  /**
+   * Scope defaults to footer as almost all JavaScript assets can be placed in
+   * the footer.
+   *
+   * @tricky this is a change from the previous behavior!
+   *
+   * @var string
+   */
+  protected $scopeDefault = 'footer';
+
+  public function setScope($scope) {
+    $this->scope = $scope;
+  }
+
+  public function getScope() {
+    return empty($this->scope) ? $this->scopeDefault : $this->scope;
+  }
+
+  public function getScopeDefault() {
+    return $this->scopeDefault;
+  }
+}
diff --git a/core/lib/Drupal/Core/Asset/JavascriptFileAsset.php b/core/lib/Drupal/Core/Asset/JavascriptFileAsset.php
new file mode 100644
index 0000000..3235e14
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/JavascriptFileAsset.php
@@ -0,0 +1,39 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Asset\JavascriptFileAsset.
+ */
+
+namespace Drupal\Core\Asset;
+
+use Drupal\Core\Asset\JavascriptAssetInterface;
+use Drupal\Core\Asset\AssetLibraryReference;
+use Drupal\Core\Asset\BaseFileAsset;
+
+class JavascriptFileAsset extends BaseFileAsset implements JavascriptAssetInterface {
+
+  protected $scope;
+
+  /**
+   * Scope defaults to footer as almost all JavaScript assets can be placed in
+   * the footer.
+   *
+   * @tricky this is a change from the previous behavior!
+   *
+   * @var string
+   */
+  protected $scopeDefault = 'footer';
+
+  public function setScope($scope) {
+    $this->scope = $scope;
+  }
+
+  public function getScope() {
+    return empty($this->scope) ? $this->scopeDefault : $this->scope;
+  }
+
+  public function getScopeDefault() {
+    return $this->scopeDefault;
+  }
+}
diff --git a/core/lib/Drupal/Core/Asset/JavascriptStringAsset.php b/core/lib/Drupal/Core/Asset/JavascriptStringAsset.php
new file mode 100644
index 0000000..c8f3767
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/JavascriptStringAsset.php
@@ -0,0 +1,38 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Asset\JavascriptStringAsset.
+ */
+
+namespace Drupal\Core\Asset;
+
+use Drupal\Core\Asset\JavascriptAssetInterface;
+use Drupal\Core\Asset\BaseStringAsset;
+
+class JavascriptStringAsset extends BaseStringAsset implements JavascriptAssetInterface {
+
+  protected $scope;
+
+  /**
+   * Scope defaults to footer as almost all JavaScript assets can be placed in
+   * the footer.
+   *
+   * @tricky this is a change from the previous behavior!
+   *
+   * @var string
+   */
+  protected $scopeDefault = 'footer';
+
+  public function setScope($scope) {
+    $this->scope = $scope;
+  }
+
+  public function getScope() {
+    return empty($this->scope) ? $this->scopeDefault : $this->scope;
+  }
+
+  public function getScopeDefault() {
+    return $this->scopeDefault;
+  }
+}
diff --git a/core/lib/Drupal/Core/Asset/StylesheetAssetInterface.php b/core/lib/Drupal/Core/Asset/StylesheetAssetInterface.php
new file mode 100644
index 0000000..9a81daf
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/StylesheetAssetInterface.php
@@ -0,0 +1,40 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Asset\StylesheetAssetInterface.
+ */
+
+namespace Drupal\Core\Asset;
+
+use Drupal\Core\Asset\AssetInterface;
+
+/**
+ * Represents a cascading stylesheet (CSS) asset.
+ */
+interface StylesheetAssetInterface extends AssetInterface {
+
+  /**
+   * Sets the media property to be applied on this stylesheet asset.
+   *
+   * @param string $type
+   *   Either a media type, or a media query.
+   *
+   * @return NULL
+   */
+  public function setMedia($type);
+
+  /**
+   * Returns the current value of the media property on this stylesheet asset.
+   *
+   * @return string
+   */
+  public function getMedia();
+
+  /**
+   * Returns the default value of the media property on this stylesheet asset.
+   *
+   * @return mixed
+   */
+  public function getMediaDefault();
+}
diff --git a/core/lib/Drupal/Core/Asset/StylesheetExternalAsset.php b/core/lib/Drupal/Core/Asset/StylesheetExternalAsset.php
new file mode 100644
index 0000000..b7dc800
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/StylesheetExternalAsset.php
@@ -0,0 +1,57 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Asset\StylesheetExternalAsset.
+ */
+
+namespace Drupal\Core\Asset;
+
+use Drupal\Core\Asset\StylesheetAssetInterface;
+use Drupal\Core\Asset\BaseExternalAsset;
+
+class StylesheetExternalAsset extends BaseExternalAsset implements StylesheetAssetInterface {
+
+  /**
+   * The media query or type to use for this asset. Defaults to 'all'.
+   *
+   * @todo inject the defaults instead of hardcoding them.
+   *
+   * @var string
+   */
+  protected $mediaDefault = 'all';
+
+  protected $media;
+
+  protected $preprocess = FALSE;
+
+  /**
+   * Returns the current value of the media property on this stylesheet asset.
+   *
+   * @return string
+   */
+  public function getMedia() {
+    return $this->media;
+  }
+
+  /**
+   * Returns the default value of the media property on this stylesheet asset.
+   *
+   * @return mixed
+   */
+  public function getMediaDefault() {
+    return $this->mediaDefault;
+  }
+
+  /**
+   * Sets the media property to be applied on this stylesheet asset.
+   *
+   * @param string $type
+   *   Either a media type, or a media query.
+   *
+   * @return NULL
+   */
+  public function setMedia($type) {
+    $this->media = $type;
+  }
+}
diff --git a/core/lib/Drupal/Core/Asset/StylesheetFileAsset.php b/core/lib/Drupal/Core/Asset/StylesheetFileAsset.php
new file mode 100644
index 0000000..38b3a6b
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/StylesheetFileAsset.php
@@ -0,0 +1,55 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Asset\StylesheetFileAsset.
+ */
+
+namespace Drupal\Core\Asset;
+
+use Drupal\Core\Asset\StylesheetAssetInterface;
+use Drupal\Core\Asset\BaseFileAsset;
+
+class StylesheetFileAsset extends BaseFileAsset implements StylesheetAssetInterface {
+
+  /**
+   * The media query or type to use for this asset. Defaults to 'all'.
+   *
+   * @todo inject the defaults instead of hardcoding them.
+   *
+   * @var string
+   */
+  protected $mediaDefault = 'all';
+
+  protected $media;
+
+  /**
+   * Returns the current value of the media property on this stylesheet asset.
+   *
+   * @return string
+   */
+  public function getMedia() {
+    return $this->media;
+  }
+
+  /**
+   * Returns the default value of the media property on this stylesheet asset.
+   *
+   * @return mixed
+   */
+  public function getMediaDefault() {
+    return $this->mediaDefault;
+  }
+
+  /**
+   * Sets the media property to be applied on this stylesheet asset.
+   *
+   * @param string $type
+   *   Either a media type, or a media query.
+   *
+   * @return NULL
+   */
+  public function setMedia($type) {
+    $this->media = $type;
+  }
+}
diff --git a/core/lib/Drupal/Core/Asset/StylesheetStringAsset.php b/core/lib/Drupal/Core/Asset/StylesheetStringAsset.php
new file mode 100644
index 0000000..639f6c1
--- /dev/null
+++ b/core/lib/Drupal/Core/Asset/StylesheetStringAsset.php
@@ -0,0 +1,57 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Asset\StylesheetStringAsset.
+ */
+
+namespace Drupal\Core\Asset;
+
+use Drupal\Core\Asset\StylesheetAssetInterface;
+use Drupal\Core\Asset\BaseStringAsset;
+
+class StylesheetStringAsset extends BaseStringAsset implements StylesheetAssetInterface {
+
+  /**
+   * The media query or type to use for this asset. Defaults to 'all'.
+   *
+   * @todo inject the defaults instead of hardcoding them.
+   *
+   * @var string
+   */
+  protected $mediaDefault = 'all';
+
+  protected $media;
+
+  protected $preprocess = FALSE;
+
+  /**
+   * Returns the current value of the media property on this stylesheet asset.
+   *
+   * @return string
+   */
+  public function getMedia() {
+    return $this->media;
+  }
+
+  /**
+   * Returns the default value of the media property on this stylesheet asset.
+   *
+   * @return mixed
+   */
+  public function getMediaDefault() {
+    return $this->mediaDefault;
+  }
+
+  /**
+   * Sets the media property to be applied on this stylesheet asset.
+   *
+   * @param string $type
+   *   Either a media type, or a media query.
+   *
+   * @return NULL
+   */
+  public function setMedia($type) {
+    $this->media = $type;
+  }
+}
diff --git a/core/modules/block/lib/Drupal/block/BlockBase.php b/core/modules/block/lib/Drupal/block/BlockBase.php
index 6efda89..c285870 100644
--- a/core/modules/block/lib/Drupal/block/BlockBase.php
+++ b/core/modules/block/lib/Drupal/block/BlockBase.php
@@ -8,6 +8,7 @@
 namespace Drupal\block;
 
 use Drupal\Component\Plugin\PluginBase;
+use Drupal\Core\Asset\AssetCollector;
 
 /**
  * Defines a base block implementation that most blocks plugins will extend.
@@ -224,4 +225,9 @@ public function submit($form, &$form_state) {
    * @see \Drupal\block\BlockBase::submit()
    */
   public function blockSubmit($form, &$form_state) {}
+
+  /**
+   * {@inheritdoc}
+   */
+  public function declareAssets(AssetCollector $collector) {}
 }
diff --git a/core/modules/block/lib/Drupal/block/BlockPluginInterface.php b/core/modules/block/lib/Drupal/block/BlockPluginInterface.php
index 1887816..74e449e 100644
--- a/core/modules/block/lib/Drupal/block/BlockPluginInterface.php
+++ b/core/modules/block/lib/Drupal/block/BlockPluginInterface.php
@@ -7,6 +7,8 @@
 
 namespace Drupal\block;
 
+use Drupal\Core\Asset\AssetCollector;
+
 /**
  * Defines the required interface for all block plugins.
  *
@@ -102,4 +104,12 @@ public function submit($form, &$form_state);
    */
   public function build();
 
+  /**
+   * Declares the assets required by this block to a collector.
+   *
+   * @param \Drupal\Core\Asset\AssetCollector $collector
+   *
+   * @return void
+   */
+  public function declareAssets(AssetCollector $collector);
 }
diff --git a/core/tests/Drupal/Tests/Core/Asset/AssetAssemblyTest.php b/core/tests/Drupal/Tests/Core/Asset/AssetAssemblyTest.php
new file mode 100644
index 0000000..4ee8134
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Asset/AssetAssemblyTest.php
@@ -0,0 +1,94 @@
+<?php
+
+/**
+ * @file
+ * Contains Drupal\Tests\Core\Asset\AssetAssemblyTest.
+ */
+
+namespace Drupal\Tests\Core\Asset;
+
+use Drupal\Core\Asset\AssetBag;
+use Drupal\Core\Asset\AssetLibrary;
+use Drupal\Core\Asset\AssetLibraryRepository;
+use Drupal\Core\Asset\AssetLibraryReference;
+use Drupal\Core\Asset\JavascriptFileAsset;
+use Drupal\Core\Asset\JavascriptStringAsset;
+use Drupal\Core\Asset\JavascriptExternalAsset;
+use Drupal\Core\Asset\StylesheetFileAsset;
+use Drupal\Core\Asset\StylesheetStringAsset;
+use Drupal\Core\Asset\StylesheetExternalAsset;
+
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * Tests assorted collection and assembly related behaviors for assets.
+ *
+ * TODO refactor all of this into proper unit tests.
+ *
+ * @group Asset
+ */
+class AssetAssemblyTest extends UnitTestCase {
+
+  public static function getInfo() {
+    return array(
+      'name' => 'Asset Assembly tests',
+      'description' => 'Tests to ensure assets declared via the various possible approaches come out with the correct properties, in the proper order.',
+      'group' => 'Asset',
+    );
+  }
+
+  public function createJQueryAssetLibrary() {
+    $library = new AssetLibrary(array(new JavascriptFileAsset('core/misc/jquery.js')));
+    return $library->setTitle('jQuery')
+      ->setVersion('1.8.2')
+      ->setWebsite('http://jquery.com');
+  }
+
+  /**
+   * Tests various simple single-bag asset assembly scenarios.
+   *
+   * Much of the real complexity of asset ordering in AssetBags comes from
+   * nesting them, but these tests are focused on the basic mechanics of
+   * assembly within a single bag.
+   */
+  public function testSingleBagAssetAssemblies() {
+    // Dead-simple bag - contains just one css and one js assets, both local files.
+    $bag = new AssetBag();
+
+    $css1 = new StylesheetFileAsset(DRUPAL_ROOT . '/core/misc/vertical-tabs.css');
+    $js1 = new JavascriptFileAsset(DRUPAL_ROOT . '/core/misc/ajax.js');
+
+    $bag->add($css1);
+    $bag->add($js1);
+
+    $this->assertTrue($bag->hasCss(), 'AssetBag correctly reports that it contains CSS assets.');
+    $this->assertTrue($bag->hasJs(), 'AssetBag correctly reports that it contains javascript assets.');
+
+    $this->assertEquals(array($css1), $bag->getCss());
+    $this->assertEquals(array($js1), $bag->getJs());
+
+    $css2 = new StylesheetFileAsset(DRUPAL_ROOT . 'core/misc/dropbutton/dropbutton.base.css');
+    $bag->add($css2);
+
+    $this->assertEquals(array($css1, $css2), $bag->getCss());
+
+    $this->assertEquals(array($css1, $js1, $css2), $bag->all());
+  }
+
+  public function testSortingAndDependencyResolution() {
+    $bag = new AssetBag();
+
+    $alm = new AssetLibraryRepository();
+    $alm->add('system', 'jquery', $this->createJQueryAssetLibrary());
+    $dep = new AssetLibraryReference('jquery', $alm);
+
+    $css1 = new StylesheetFileAsset(DRUPAL_ROOT . '/core/misc/vertical-tabs.css');
+    $js1 = new JavascriptFileAsset(DRUPAL_ROOT . '/core/misc/ajax.js');
+    // $js1->addDependency($dep);
+
+    $bag->add($css1);
+    $bag->add($js1);
+
+    $this->assertEquals(array(new JavascriptFileAsset('core/misc/jquery.js'), $js1), $bag->getJs());
+  }
+}
diff --git a/core/tests/Drupal/Tests/Core/Asset/AssetBagTest.php b/core/tests/Drupal/Tests/Core/Asset/AssetBagTest.php
new file mode 100644
index 0000000..4246e92
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Asset/AssetBagTest.php
@@ -0,0 +1,34 @@
+<?php
+/**
+ * @file
+ * Contains Drupal\Tests\Core\Asset\AssetBagTest.
+ */
+
+
+namespace Drupal\Tests\Core\Asset;
+
+use Drupal\Tests\UnitTestCase;
+
+
+/**
+ * TODO all of it
+ * @group Asset
+ */
+class AssetBagTest extends UnitTestCase {
+
+  public static function getInfo() {
+    return array(
+      'name' => '', // TODO give me a name
+      'description' => '', // TODO give me a description
+      'group' => '', // TODO give me the same group as above
+    );
+  }
+
+  public function setUp() {
+    parent::setUp();
+  }
+
+  public function testStub() {
+    // TODO anything. without this, phpunit blows up.
+  }
+}
diff --git a/core/tests/Drupal/Tests/Core/Asset/AssetCollectorTest.php b/core/tests/Drupal/Tests/Core/Asset/AssetCollectorTest.php
new file mode 100644
index 0000000..479adf9
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Asset/AssetCollectorTest.php
@@ -0,0 +1,231 @@
+<?php
+/**
+ * @file
+ * Contains Drupal\Tests\Core\Asset\AssetCollectorTest.
+ */
+
+namespace Drupal\Tests\Core\Asset;
+
+if (!defined('CSS_AGGREGATE_THEME')) {
+  define('CSS_AGGREGATE_THEME', 100);
+}
+
+if (!defined('CSS_AGGREGATE_DEFAULT')) {
+  define('CSS_AGGREGATE_DEFAULT', 0);
+}
+
+if (!defined('JS_DEFAULT')) {
+  define('JS_DEFAULT', 0);
+}
+
+use Drupal\Core\Asset\AssetBag;
+use Drupal\Core\Asset\AssetCollector;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * Tests for the asset collector.
+ *
+ * TODO DOCS, DOCS, DOCS DOCS DOCS
+ *
+ * @group Asset
+ */
+class AssetCollectorTest extends UnitTestCase {
+
+  /**
+   * @var \Drupal\Core\Asset\AssetCollector
+   */
+  protected $collector;
+
+  protected $builtinDefaults = array(
+    'css' => array(
+      'group' => CSS_AGGREGATE_DEFAULT,
+      'weight' => 0,
+      'every_page' => FALSE,
+      'media' => 'all',
+      'preprocess' => TRUE,
+      'browsers' => array(
+        'IE' => TRUE,
+        '!IE' => TRUE,
+      ),
+    ),
+    'js' => array(
+      'group' => JS_DEFAULT,
+      'every_page' => FALSE,
+      'weight' => 0,
+      'scope' => 'header',
+      'cache' => TRUE,
+      'preprocess' => TRUE,
+      'attributes' => array(),
+      'version' => NULL,
+      'browsers' => array(),
+    ),
+  );
+
+
+  public static function getInfo() {
+    return array(
+      'name' => 'Asset Collector tests',
+      'description' => 'Tests that the AssetCollector system works correctly.',
+      'group' => 'Asset',
+    );
+  }
+
+  public function setUp() {
+    parent::setUp();
+    $this->collector = new AssetCollector();
+  }
+
+  /**
+   * Tests that the collector injects provided metadata to created assets.
+   */
+  public function testMetadataInjection() {
+    // Test a single value first
+    $asset = $this->collector->create('css', 'file', 'foo', array('group' => CSS_AGGREGATE_THEME));
+    $this->assertEquals(CSS_AGGREGATE_THEME, $asset['group'], 'Collector injected user-passed parameters into the created asset.');
+
+    // TODO is it worth testing multiple params? what about weird ones, like weight?
+  }
+
+  /**
+   * @expectedException Exception
+   */
+  public function testExceptionOnAddingAssetWithoutBagPresent() {
+    $asset = $this->collector->create('css', 'string', 'foo');
+    $this->collector->add($asset);
+  }
+
+  /**
+   * TODO separate test for an explicit add() call.
+   */
+  public function testAssetsImplicitlyArriveInInjectedBag() {
+    $bag = new AssetBag();
+    $this->collector->setBag($bag);
+
+    $asset2 = $this->collector->create('css', 'file', 'bar');
+    $this->assertContains($asset2, $bag->getCss(), 'Created asset was implicitly added to bag.');
+  }
+
+  /**
+   * @expectedException Exception
+   */
+  public function testClearBag() {
+    $bag = new AssetBag();
+    $this->collector->setBag($bag);
+    $this->collector->clearBag();
+
+    $this->collector->add($this->collector->create('css', 'file', 'bar'));
+  }
+
+  public function testLock() {
+    $this->assertTrue($this->collector->lock($this), 'Collector locked successfully.');
+    $this->assertTrue($this->collector->isLocked(), 'Collector accurately reports that it is locked via isLocked() method.');
+  }
+
+  public function testUnlock() {
+    $this->collector->lock($this);
+    $this->assertTrue($this->collector->unlock($this), 'Collector unlocked successfully when appropriate key was provided.');
+    $this->assertFalse($this->collector->isLocked(), 'Collector correctly reported unlocked state via isLocked() method after unlocking.');
+  }
+
+  /**
+   * @expectedException Exception
+   */
+  public function testUnlockFailsWithoutCorrectSecret() {
+    $this->collector->lock('foo');
+    $this->collector->unlock('bar');
+  }
+
+  /**
+   * @expectedException Exception
+   */
+  public function testLockingPreventsSettingDefaults() {
+    $this->collector->lock($this);
+    $this->collector->setDefaults('css', array('foo' => 'bar'));
+  }
+
+  /**
+   * @expectedException Exception
+   */
+  public function testLockingPreventsRestoringDefaults() {
+    $this->collector->lock($this);
+    $this->collector->restoreDefaults();
+  }
+
+  /**
+   * @expectedException Exception
+   */
+  public function testLockingPreventsClearingBag() {
+    $this->collector->lock($this);
+    $this->collector->clearBag();
+  }
+
+  /**
+   * @expectedException Exception
+   */
+  public function testLockingPreventsSettingBag() {
+    $this->collector->lock($this);
+    $this->collector->setBag(new AssetBag());
+  }
+
+  public function testBuiltinDefaultAreTheSame() {
+    $this->assertEquals($this->builtinDefaults, $this->collector->getDefaults(), 'Expected set of built-in defaults reside in the collector.');
+  }
+
+  public function testChangeAndRestoreDefaults() {
+    $changed_defaults = array('every_page' => TRUE, 'group' => CSS_AGGREGATE_THEME);
+    $this->collector->setDefaults('css', $changed_defaults);
+    $this->assertEquals($changed_defaults + $this->builtinDefaults['css'], $this->collector->getDefaults('css'), 'Expected combination of built-in and injected defaults reside in the collector.');
+
+    $this->collector->restoreDefaults();
+    $this->assertEquals($this->builtinDefaults, $this->collector->getDefaults(), 'Built-in defaults were correctly restored.');
+
+  }
+
+  /**
+   * @expectedException InvalidArgumentException
+   */
+  public function testGetNonexistentDefault() {
+    $this->collector->getDefaults('foo');
+    $this->fail('No exception thrown when an invalid key was requested.');
+  }
+
+  public function testDefaultPropagation() {
+    // Test that defaults are correctly applied by the factory.
+    $this->collector->setDefaults('css', array('every_page' => TRUE, 'group' => CSS_AGGREGATE_THEME));
+    $css1 = $this->collector->create('css', 'file', 'foo');
+    $this->assertTrue($css1['every_page'], 'Correct default propagated for "every_page" property.');
+    $this->assertEquals(CSS_AGGREGATE_THEME, $css1['group'], 'Correct default propagated for "group" property.');
+
+    // TODO bother testing js? it seems logically redundant
+  }
+
+  public function testCreateStylesheetFileAsset() {
+    $css_file1 = $this->collector->create('css', 'file', 'foo');
+    $this->assertInstanceOf('\Drupal\Core\Asset\StylesheetFileAsset', $css_file1, 'Collector correctly created a StylesheetFileAsset instance.');
+  }
+
+  public function testCreateStylesheetExternalAsset() {
+    $css_external1 = $this->collector->create('css', 'external', 'http://foo.bar/path/to/asset.css');
+    $this->assertInstanceOf('\Drupal\Core\Asset\StylesheetExternalAsset', $css_external1, 'Collector correctly created a StylesheetExternalAsset instance.');
+  }
+
+  public function testCreateStylesheetStringAsset() {
+    $css_string1 = $this->collector->create('css', 'string', 'foo');
+    $this->assertInstanceOf('\Drupal\Core\Asset\StylesheetStringAsset', $css_string1, 'Collector correctly created a StylesheetStringAsset instance .');
+  }
+
+  public function testCreateJavascriptFileAsset() {
+    $js_file1 = $this->collector->create('js', 'file', 'foo');
+    $this->assertInstanceOf('\Drupal\Core\Asset\JavascriptFileAsset', $js_file1, 'Collector correctly created a JavascriptFileAsset instance .');
+  }
+
+  public function testCreateJavascriptExternalAsset() {
+    $js_external1 = $this->collector->create('js', 'external', 'http://foo.bar/path/to/asset.js');
+    $this->assertInstanceOf('\Drupal\Core\Asset\JavascriptExternalAsset', $js_external1, 'Collector correctly created a JavascriptExternalAsset instance .');
+  }
+
+  public function testCreateJavascriptStringAsset() {
+    $js_string1 = $this->collector->create('js', 'string', 'foo');
+    $this->assertInstanceOf('\Drupal\Core\Asset\JavascriptStringAsset', $js_string1, 'Collector correctly created a JavascriptStringAsset instance .');
+  }
+}
\ No newline at end of file
diff --git a/core/tests/Drupal/Tests/Core/Asset/AssetLibraryManagerTest.php b/core/tests/Drupal/Tests/Core/Asset/AssetLibraryManagerTest.php
new file mode 100644
index 0000000..59a7b11
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Asset/AssetLibraryManagerTest.php
@@ -0,0 +1,31 @@
+<?php
+/**
+ */
+
+namespace Drupal\Tests\Core\Asset;
+
+use Drupal\Tests\UnitTestCase;
+
+
+/**
+ *
+ * @group TODO add a group
+ */
+class AssetLibraryManagerTest extends UnitTestCase {
+
+  public static function getInfo() {
+    return array(
+      'name' => '', // TODO give me a name
+      'description' => '', // TODO give me a description
+      'group' => '', // TODO give me the same group as above
+    );
+  }
+
+  public function setUp() {
+    parent::setUp();
+  }
+
+  public function testStub() {
+    // TODO anything. without this, phpunit blows up.
+  }
+}
diff --git a/core/tests/Drupal/Tests/Core/Asset/AssetLibraryTest.php b/core/tests/Drupal/Tests/Core/Asset/AssetLibraryTest.php
new file mode 100644
index 0000000..fc3ff96
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Asset/AssetLibraryTest.php
@@ -0,0 +1,96 @@
+<?php
+/**
+ * @file
+ * Contains Drupal\Tests\Core\Asset\AssetLibraryTest.
+ */
+
+namespace Drupal\Tests\Core\Asset;
+
+use Drupal\Core\Asset\AssetLibrary;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ *
+ * @group Asset
+ */
+class AssetLibraryTest extends UnitTestCase {
+
+  public static function getInfo() {
+    return array(
+      'name' => 'Asset Library tests',
+      'description' => 'Tests that the AssetLibrary behaves correctly.',
+      'group' => 'Asset',
+    );
+  }
+
+  public function getLibraryFixture() {
+    $library = new AssetLibrary();
+    $library->setTitle('foo')
+      ->setVersion('1.2.3')
+      ->setWebsite('http://foo.bar')
+      ->addDependency('foo', 'bar');
+    return $library;
+  }
+
+  public function testConstructorValueInjection() {
+    $values = array(
+      'title' => 'foo',
+      'version' => '1.2.3',
+      'website' => 'http://foo.bar',
+      'dependencies' => array(array('foo', 'bar')),
+    );
+    $library = new AssetLibrary($values);
+
+    $fixture = $this->getLibraryFixture();
+    $this->assertEquals($fixture->getTitle(), $library->getTitle(), 'Title passed correctly through the constructor.');
+    $this->assertEquals($fixture->getVersion(), $library->getVersion(), 'Version passed correctly through the constructor.');
+    $this->assertEquals($fixture->getWebsite(), $library->getWebsite(), 'Website passed correctly through the constructor.');
+    $this->assertEquals($fixture->getDependencies(), $library->getDependencies(), 'Dependencies information passed correctly through the constructor.');
+  }
+
+  public function testAddDependency() {
+    $library = $this->getLibraryFixture();
+    $library->addDependency('baz', 'bing');
+    $this->assertEquals($library->getDependencies(), array(array('foo', 'bar'), array('baz', 'bing')), 'Dependencies added to library successfully.');
+  }
+
+  public function testClearDependencies() {
+    $library = $this->getLibraryFixture();
+    $library->clearDependencies();
+    $this->assertEmpty($library->getDependencies(), 'Dependencies recorded in the library were cleared correctly.');
+  }
+
+  public function testFrozenNonwriteability() {
+    $library = $this->getLibraryFixture();
+    $library->freeze();
+    try {
+      $library->setTitle('bar');
+      $this->fail('No exception thrown when attempting to set a new title on a frozen library.');
+    }
+    catch (\LogicException $e) {}
+
+    try {
+      $library->setVersion('2.3.4');
+      $this->fail('No exception thrown when attempting to set a new version on a frozen library.');
+    }
+    catch (\LogicException $e) {}
+
+    try {
+      $library->setWebsite('http://bar.baz');
+      $this->fail('No exception thrown when attempting to set a new website on a frozen library.');
+    }
+    catch (\LogicException $e) {}
+
+    try {
+      $library->addDependency('bing', 'bang');
+      $this->fail('No exception thrown when attempting to add a new dependency on a frozen library.');
+    }
+    catch (\LogicException $e) {}
+
+    try {
+      $library->clearDependencies();
+      $this->fail('No exception thrown when attempting to clear dependencies from a frozen library.');
+    }
+    catch (\LogicException $e) {}
+  }
+}
diff --git a/core/tests/Drupal/Tests/Core/Asset/AssetMetadataTest.php b/core/tests/Drupal/Tests/Core/Asset/AssetMetadataTest.php
new file mode 100644
index 0000000..b06b9a0
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Asset/AssetMetadataTest.php
@@ -0,0 +1,52 @@
+<?php
+/**
+ * @file
+ * Contains Drupal\Tests\Core\Asset\AssetMetadataTest.
+ */
+
+namespace Drupal\Tests\Core\Asset;
+
+use Drupal\Core\Asset\AssetMetadataBag;
+use Drupal\Core\Asset\StylesheetFileAsset;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * Tests that metadata is correctly handled by asset objects.
+ */
+class AssetMetadataTest extends UnitTestCase {
+
+  public static function getInfo() {
+    return array(
+      'name' => 'Asset Metadata Tests',
+      'description' => 'Tests that asset classes handle their metadata and defaults correctly.',
+      'group' => 'Asset',
+    );
+  }
+
+  public function testDefaultsOverriddenByExplicitValues() {
+    // As this logic is implemented on the common parent, BaseAsset, testing
+    // one type of asset is sufficient.
+    $asset = new StylesheetFileAsset('foo', array('group' => CSS_AGGREGATE_THEME, 'every_page' => TRUE));
+    $defaults = array(
+      'group' => CSS_AGGREGATE_DEFAULT,
+      'weight' => 0,
+      'every_page' => FALSE,
+      'media' => 'all',
+      'preprocess' => TRUE,
+      'browsers' => array(
+        'IE' => TRUE,
+        '!IE' => TRUE,
+      ),
+    );
+    $asset->setDefaults($defaults);
+
+    foreach ($defaults as $key => $value) {
+      if (in_array($key, array('group', 'every_page'))) {
+        $this->assertNotEquals($value, $asset[$key], 'Explicit value correctly overrides default.');
+      }
+      else {
+        $this->assertEquals($value, $asset[$key], 'Default value comes through when no explicit value is present.');
+      }
+    }
+  }
+}
\ No newline at end of file
diff --git a/core/tests/Drupal/Tests/Core/Asset/AssetTest.php b/core/tests/Drupal/Tests/Core/Asset/AssetTest.php
new file mode 100644
index 0000000..2752d8c
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Asset/AssetTest.php
@@ -0,0 +1,37 @@
+<?php
+/**
+ * @file
+ *
+ * Contains Drupal\Tests\Core\Asset\AssetTest.
+ */
+
+namespace Drupal\Tests\Core\Asset;
+
+use Drupal\Tests\UnitTestCase;
+
+
+/**
+ * Tests for the base asset classes.
+ *
+ * TODO all of it.
+ *
+ * @group Asset
+ */
+class AssetTest extends UnitTestCase {
+
+  public static function getInfo() {
+    return array(
+      'name' => 'Asset tests',
+      'description' => 'Unit tests for all base asset classes.',
+      'group' => 'Asset',
+    );
+  }
+
+  public function setUp() {
+    parent::setUp();
+  }
+
+  public function testStub() {
+    // TODO anything. without this, phpunit blows up.
+  }
+}