code: def _is_custom_manager_attribute(node):
      
  
      attrname = node.attrname
      if not name_is_from_qs(attrname):
          return False
  
      for attr in node.get_children():
          inferred = safe_infer(attr)
          funcdef = getattr(inferred, '_proxied', None)
          if _is_custom_qs_manager(funcdef):
              return True
  
      return False
docs: Checks if the attribute is a valid attribute for a queryset manager.