docs: def encrypt_file_inline(filename, passphrase):
      """Encrypt file inline, with an optional passphrase.
  
      If you set the passphrase to None, a default is used.
      This will make you vulnerable to confirmation attacks
      and learn-partial-information attacks.
  
      :param filename: The name of the file to encrypt.
      :type filename: str
      :param passphrase: The passphrase used to decrypt the file.
      :type passphrase: str or None
      :returns: The key required to decrypt the file.
      :rtype: str
      """
      key = key_generators.key_from_file(filename, passphrase)
  
      inline_transform(filename, key)
  
      return key