docs: def build_backend(self, backend_node):
          """parse `backend` sections
  
          Args:
              backend_node (TreeNode): Description
  
          Returns:
              config.Backend: an object
          """
          proxy_name = backend_node.backend_header.proxy_name.text
          config_block_lines = self.__build_config_block(
              backend_node.config_block)
          return config.Backend(name=proxy_name, config_block=config_block_lines)