docs: def from_config(cls, name, config):
          """
          Behaves like the base Configurable class's `from_config()` except this
          makes sure that the `Pluggable` subclass with the given name is
          actually a properly installed plugin first.
          """
          installed_classes = cls.get_installed_classes()
  
          if name not in installed_classes:
              raise ValueError("Unknown/unavailable %s" % cls.__name__.lower())
  
          pluggable_class = installed_classes[name]
  
          pluggable_class.validate_config(config)
  
          instance = pluggable_class()
          if not instance.name:
              instance.name = name
          instance.apply_config(config)
  
          return instance