Obviously not ideal, but it could for instance come up when the file format has one overall endianness but wants to include fragments of data conventionally enc

Obviously not ideal, but it could for instance come up when the file format has one overall endianness but wants to include fragments of data conventionally encoded with the opposite endianness. Trivial example would be a .tar file containing an assortment of other files, but this would also include say embedding network endian data or images within a larger file that contains other data.