code: def validate_bbox(s):
      if isinstance(s, str):
          s = s.lower()
          if s == "tight":
              return s
          if s == "standard":
              return None
          raise ValueError("bbox should be 'tight' or 'standard'")
      elif s is not None:
          # Backwards compatibility. None is equivalent to 'standard'.
          raise ValueError("bbox should be 'tight' or 'standard'")
      return s
  
imports: import ast
  from functools import lru_cache, reduce
  from numbers import Real
  import operator
  import os
  import re
  import numpy
  from matplotlib import _api, cbook
  from matplotlib.cbook import ls_mapper
  from matplotlib.colors import Colormap, is_color_like
  from matplotlib._fontconfig_pattern import parse_fontconfig_pattern
  from matplotlib._enums import JoinStyle, CapStyle
  from cycler import Cycler, cycler
label_desc: Use image node_id 30 for calling a global function with example usage: validate_bbox(s) and returns: s, s, None