In the "Why Xar" page of the Xar Google Code page it says:
Additionally, this means xar can use different compression methods for each file in the archive. For instance, it might not be a good idea to try to try to compress an already compressed file, but a large file might benefit greatly from using bzip2, whereas a small text file would be better served to use gzip.
I read the man page and it does not indicates how to do this. So, does anyone know how?