The DJVU format is quite extensible by adding new chunk types.
Old viewers will simply ignore them.
As long as the remaining chunks contain enough data,
old viewers can display an image regardless of the
The main use of the version number in DJVU files
was to trigger plugin updates. Early viewers suggest
to download a new version when they see DJVU
documents with a higher version numbers.
This was intended for critical updates and
incompatible format changes.
The system has been disabled in the djvulibre plugins
because unnecessary version number increases
were causing more trouble than necessary.
The djvulibre viewers now ignore the version numbers
and simply try to interpret what they understand.
I suspect the LT viewers no longer inspect the
version number either.
The SDJVU files cannot be confused with DjVu files
because they do not contain any chunk we can read.
In fact this is simply an encapsulation of the
standard DJVU data.
See the file doc/djvuchanges.txt in the djvulibre distribution.
http://djvu.cvs.sourceforge.net/djvu/dj ... ision=HEAD