Siblings Identifiers of the passage

        :rtype: (str, str)

def siblingsId(self) -> Tuple[CtsReference, CtsReference]:
        """ Siblings Identifiers of the passage

        :rtype: (str, str)
        """
        self._raise_depth()

        if not self._text:
            raise MissingAttribute("CapitainsCtsPassage was initiated without CtsTextMetadata object")
        if self._prev_next:
            return self._prev_next

        document_references = self._text.getReffs(level=self.depth)

        if self.reference.is_range():
            start, end = self.reference.start, self.reference.end
            range_length = len(self.getReffs(level=0))
        else:
            start = end = self.reference.start
            range_length = 1

        start = document_references.index(start)
        end = document_references.index(end)

        if start == 0:
            # If the passage is already at the beginning
            _prev = None
        elif start - range_length < 0:
            if start == end:
                _prev = document_references[0]
            else:
                _prev = "{}-{}".format(document_references[0], document_references[start-1])
        else:
            if start == end:
                _prev = document_references[start-1]
            else:
                _prev = "{}-{}".format(document_references[start-range_length], document_references[start-1])

        if start + 1 == len(document_references) or end + 1 == len(document_references):
            # If the passage is already at the end
            _next = None
        elif end + range_length > len(document_references):
            if start == end:
                _next = document_references[-1]
            else:
                _next = "{}-{}".format(document_references[end+1], document_references[-1])
        else:
            if start == end:
                _next = document_references[end+1]
            else:
                _next = "{}-{}".format(document_references[end+1], document_references[end + range_length])

        self._prev_next = (CtsReference(_prev), CtsReference(_next))
        return self._prev_next