code: def _is_control(char: str) -> bool:
      r"""Checks whether `char` is a control character.
  
      Note: this function is not standard and should be considered for BERT
      tokenization only. See the comments for more details.
      """
      # These are technically control characters but we count them as whitespace
      # characters.
      if char in ("\t", "\n", "\r"):
          return False
      cat = unicodedata.category(char)
      if cat.startswith("C"):
          return True
      return False
  
file_path: texar/texar/tf/data/tokenizers/bert_tokenizer_utils.py
imports: from typing import Dict, List, Optional
  import collections
  import unicodedata
label_desc: Use image node_id 4 for calling a global function with example usage: _is_control(char) and returns: False, False, True