$registry = new WebAssetRegistry;
$registry->add(new WebAssetItem('mother'));
$registry->add(new WebAssetItem('father'));
$registry->add(new WebAssetItem('child1', ['dependencies' => ['mother', 'father']]));

$manager = new WebAssetManager($registry );
$manager->enableAsset('child1'); // Will enable 'child1' asset and all its 'dependencies'
$manager->enableAsset('foo'); // Throw an exception UnknownAsset
$registry->add(new WebAssetItem('foo'));
$manager->enableAsset('foo'); // Will NOT throw an exception UnknownAsset :)

// Check if asset available in registry without an exception
if ($registry->exists('bar'))
{
    $manager->enableAsset('bar');
}

// Get WebAsset manager instance
$wa = CMSFactory::getDocument()->getWebAssetManager();

// Enable asset
$wa->enableAsset('foo');

// Add new asset on runtime
$wr = $wa->getRegistry();
$wr->add(new WebAssetItem('bar'));

// Add a custom registry file joomla.asset.json
$wr->addRegistryFile($path);