code: def getPrevNextUrn(self, reference):
          
          _prev, _next = _SharedMethod.prevnext(
              self.retriever.getPrevNextUrn(
                  urn="{}:{}".format(
                      str(
                          URN(
                              str(self.urn)).upTo(URN.NO_PASSAGE)
                      ),
                      str(reference)
                  )
              )
          )
          return _prev, _next
docs: Get the previous URN of a reference of the text
  
          :param reference: CtsReference from which to find siblings
          :type reference: Union[CtsReference, str]
          :return: (Previous CapitainsCtsPassage CtsReference,Next CapitainsCtsPassage CtsReference)