def current(self,index=None):
        """Get the current authoritative annotation (used with suggestions in a structural context)

        This returns only one annotation if multiple exist, use `index` to select another in the sequence.

        Returns:
            an annotation element (:class:`AbstractElement`)

        Raises:
            :class:`NoSuchAnnotation`
        """
        if index is None:
            try:
                return next(self.select(Current,None,False))
            except StopIteration:
                raise NoSuchAnnotation
        else:
            for e in self.select(Current,None,False):
                return e[index]
            raise NoSuchAnnotation