input: from typing import Any
  
  def read_data_from_json(filename: str) -> Any:
      """ Read data from a JSON file and handle potential errors related to file
      not found and invalid JSON format.
      >>> read_data_from_json('non_existent_file.json')
      'The file specified does not exist.'
      >>> read_data_from_json('invalid_json_file.json')
      'The file specified is not in a valid JSON format.'
      >>> read_data_from_json('valid_json_file.json')
      {...} # actual JSON content from the file
      """
output:     import json
      import os
  
      if not os.path.exists(filename):
          return 'The file specified does not exist.'
      
      try:
          with open(filename, 'r') as file:
              data = json.load(file)
              return data
      except json.JSONDecodeError:
          return 'The file specified is not in a valid JSON format.'