def is_value_known(self):
<EOL>return self._kwargs['<STR_LIT>']<EOL>
Tests if an existing value is known for this data element.

        If it is known that a value does not exist, then this method
        returns ``true``.

        return: (boolean) - ``true`` if the element value is known,
                ``false`` if the element value is not known
        *compliance: mandatory -- This method must be implemented.*