The javap tool must be updated to enable selection of versioned class files.

Currently
     $ javap -cp version.jar version.Version

will display the attributes of the base entry in a multi-release jar file (i.e. version/Version.class). If one wants to inspect versioned entries they need to specifically request a class through a jar url as in

     $ javap jar:file:version.jar\!/META-INF/versions/9/version/Version.class

What we'd like to do is add a command line option to select the appropriate version of the class.

It turns out that javap already has such a command line option, -multi-release. So one can select appropriate classes like this:

    $ javap -cp version.jar version.Version (for the base version)
    $ javap -cp version.jar -multi-release 9 version.Version (for the jdk 9 version)
    $ javap -cp version.jar -multi-release runtime version.Version (also for the jdk 9 version since runtime is equivalent to 9 on jdk 9)

So all we really need to do is to document the option.