Starting from V6, plugin metadata must be declared via Manifest.xml

Starting from V6, there must be a Manifest.xml file in the plugin folder, which specifies the plugin file name, the plugin class name, the API version used by the plugin, and other parameters that were previously specified using attributes on the plugin class. For V4 and V5, the presence of a manifest is not required, the previous option with attributes is supported, but if a manifest is present, it will be used. More details in the article about folder structure.