code: def _text2bool(val):
      
      lval = val.lower()
      if lval in __true_strings: return True
      if lval in __false_strings: return False
      raise ValueError("Invalid value for boolean option: %s" % val)
docs: Converts strings to True/False depending on the 'truth' expressed by
      the string. If the string can't be converted, the original value
      will be returned.
  
      See '__true_strings' and '__false_strings' for values considered
      'true' or 'false respectively.
  
      This is usable as 'converter' for SCons' Variables.