code: def _parse_marker_var(tokenizer: Tokenizer) -> MarkerVar:
      """
      marker_var = VARIABLE | QUOTED_STRING
      """
      if tokenizer.check("VARIABLE"):
          return process_env_var(
              tokenizer.read().text.replace(".", "_")
          )
      elif tokenizer.check("QUOTED_STRING"):
          return process_python_str(tokenizer.read().text)
      else:
          tokenizer.raise_syntax_error(
              message="Expected a marker variable or quoted string"
          )
  
imports: import ast
  from typing import Any, List, NamedTuple, Optional, Tuple, Union
  from ._tokenizer import DEFAULT_RULES, Tokenizer
label_desc: Use image node_id 13 for calling a global function with example usage: _parse_marker_var(tokenizer) and returns: process_env_var, process_python_str