bclose := bytealg.IndexByteString(srcs, ']')
				if bclose == -1 {
					conf.err = errors.New("unclosed criterion bracket")
					return conf
				}
				var err error
				criteria, err = parseCriteria(srcs[1:bclose])
				if err != nil {
					conf.err = errors.New("invalid criteria: " + srcs[1:bclose])
					return conf
				}
				srcs = srcs[bclose+1:]
			}
			if conf.sources == nil {