@abc.abstractmethod<EOL><INDENT>def has_value(self):<DEDENT>
return<EOL>
Tests if this data element has a set non-default value.

        :return: ``true`` if this element value has been set, ``false`` otherwise
        :rtype: ``boolean``
        :raise: ``IllegalState`` -- ``is_value_known()`` is ``false``

        *compliance: mandatory -- This method must be implemented.*