def get_duration_set(self):
<EOL>if self._kwargs['<STR_LIT>'] not in ['<STR_LIT>']:<EOL><INDENT>raise errors.IllegalState()<EOL><DEDENT>return self._kwargs['<STR_LIT>']<EOL>
Gets the set of acceptable duration values.

        return: (osid.calendaring.Duration) - a set of durations or an
                empty array if not restricted
        raise:  IllegalState - syntax is not a ``DURATION``
        *compliance: mandatory -- This method must be implemented.*