parameters: (self, checker, message)
docstring: Constructor to create all validators.
  
      Args:
        checker: function to verify the constraint.
          Input of this method varies, see SimpleValidator and
            DictionaryValidator for a detailed description.
        message: string, error message to be shown to the user
docstring_summary: Constructor to create all validators.
docstring_tokens: Constructor to create all validators .
function: def __init__(self, checker, message):
      """Constructor to create all validators.
  
      Args:
        checker: function to verify the constraint.
          Input of this method varies, see SimpleValidator and
            DictionaryValidator for a detailed description.
        message: string, error message to be shown to the user
      """
      self.checker = checker
      self.message = message
      Validator.validators_count += 1
      # Used to assert validators in the order they were registered (CL/18694236)
      self.insertion_index = Validator.validators_count
function_tokens: def __init__ ( self , checker , message ) : self . checker = checker self . message = message Validator . validators_count += 1 # Used to assert validators in the order they were registered (CL/18694236) self . insertion_index = Validator . validators_count