code: def concat(docs: Sequence[Doc]) -> Doc:
      """Concatenation of documents."""
      docs = list(docs)
      if len(docs) == 1:
          return docs[0]
      return _ConcatDoc(docs)
  
imports: from __future__ import annotations
  import abc
  from collections.abc import Sequence
  import enum
  from functools import partial
  import sys
  from typing import NamedTuple
  from jax._src import config
label_desc: Use image node_id 9 for calling a global function with example usage: concat(docs) and returns: _ConcatDoc, docs