Each new release redefines the "alias" classes in the package
"ibook.release" to refer
to implementation classes in a version-specific package such as "ibook.v10".
For example, in the v10 release of IDVI the applet "ibook.release.IDVIOnePageApplet"
is a trivial extension of the class "ibook.v10.idvi.DVIOnePageApplet".
This ensures that all classes which interact with each other are tagged with a version
number as part of their class name, so that no mixing of old and new classes occurs,
while not requiring the modification of existing html files when a new release is