visadForm(?).save

I was recently bitten by a problem with
visadform().save(file,dataobject)

I saved some data, Updated visad.jar and then I could not read the
dataobjects back in because the underlying data object class was
changed.

There is an other version: visadform(1).save(file,dataobject).
This saves something called a bianary object.  The documentation does
not realy explain what that means.  Is this designed so that I could
read back files even if the underlying data object class had changed?

thanks for any suggestions