docs: def _connect_signal(self, index):
          """Create signals for building indexes."""
          post_save_signal = ElasticSignal(index, 'build')
          post_save_signal.connect(post_save, sender=index.object_type)
          self.signals.append(post_save_signal)
  
          post_delete_signal = ElasticSignal(index, 'remove_object')
          post_delete_signal.connect(post_delete, sender=index.object_type)
          self.signals.append(post_delete_signal)
  
          # Connect signals for all dependencies.
          for dependency in index.get_dependencies():
              # Automatically convert m2m fields to dependencies.
              if isinstance(dependency, (models.ManyToManyField, ManyToManyDescriptor)):
                  dependency = ManyToManyDependency(dependency)
              elif not isinstance(dependency, Dependency):
                  raise TypeError("Unsupported dependency type: {}".format(repr(dependency)))
  
              signal = dependency.connect(index)
              self.signals.extend(signal)