* Plugin definition mappers provide an API for handling untyped array plugin definitions. See [this issue](http://drupal.org/node/2458789) for an effort to fix this in core's plugin system.* Plugin selectors allow users to select plugins of a particular type and configure them using the plugins' configuration forms.* Filtered plugin manager decorators to easily filter/limit the plugins a manager can provide.* A plugin collection field type that allows plugin instances to be stored on content entities.