Executes a command against the underlying HTML element.

        Args:
          command: The name of the command to _execute as a string.
          params: A dictionary of named parameters to send with the command.

        Returns:
          The command's JSON response loaded into a dictionary object.

def _execute(self, command, params=None):
        """Executes a command against the underlying HTML element.

        Args:
          command: The name of the command to _execute as a string.
          params: A dictionary of named parameters to send with the command.

        Returns:
          The command's JSON response loaded into a dictionary object.
        """
        if not params:
            params = {}
        params['id'] = self._id
        return self._parent.execute(command, params)