code: def _check_svcaller(item):
      
      allowed = set(reduce(operator.add, [list(d.keys()) for d in structural._CALLERS.values()]) + [None, False])
      svs = item["algorithm"].get("svcaller")
      if not isinstance(svs, (list, tuple)):
          svs = [svs]
      problem = [x for x in svs if x not in allowed]
      if len(problem) > 0:
          raise ValueError("Unexpected algorithm 'svcaller' parameters: %s\n"
                           "Supported options: %s\n" % (" ".join(["'%s'" % x for x in problem]),
                                                        sorted(list(allowed))))
docs: Ensure the provide structural variant caller is valid.