yii\BaseYii::getRootAlias PHP Method

    public static function getRootAlias($alias)
    {
        $pos = strpos($alias, '/');
        $root = $pos === false ? $alias : substr($alias, 0, $pos);
        if (isset(static::$aliases[$root])) {
            if (is_string(static::$aliases[$root])) {
                return $root;
            } else {
                foreach (static::$aliases[$root] as $name => $path) {
                    if (strpos($alias . '/', $name . '/') === 0) {
                        return $name;
                    }
                }
            }
        }
        return false;
    }