class_docstr: Tokenizes by making a request to the proxy server with REST endpoint: `/api/tokenize`.
code: def end_of_text_token(self) -> str:
      # TODO: I'm not sure what their end of text token is. I don't think it's documented.
      return " "
  
imports: import re
  from typing import List, Optional, Tuple
  from urllib.parse import unquote
  from helm.common.tokenization_request import TokenizationRequest, TokenizationRequestResult, TokenizationToken, TextRange
  from .window_service import WindowService, EncodeResult
  from .tokenizer_service import TokenizerService
  from .gpt2_window_service import GPT2WindowService
label_desc: Use image node_id 5 for calling the AI21WindowService obj's underlying member method code with example usage: obj.end_of_text_token() and returns: str