public static function embed(&$collection, $relations) {
		$tree = Set::expand(array_fill_keys(array_keys(Set::normalize($relations)), []));

		foreach ($tree as $name => $subtree) {
			$rel = static::relations($name);
			$to = $rel->to();
			$related = $rel->embed($collection, isset($relations[$name]) ? $relations[$name] : []);

			$subrelations = [];
			foreach ($relations as $path => $value) {
				if (preg_match('~^'.$name.'\.(.*)$~', $path, $matches)) {
					$subrelations[] = $matches[1];
				}
			}
			if ($subrelations) {
				$to::embed($related, $subrelations);
			}
		}
		return $collection;
	}