From the JShell help, and other documentation, it is not immediately clear what "remote runtime system" means:
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$ jshell --help
...
    -J<flag> Pass <flag> directly to the runtime system.
                            Use one -J for each runtime flag or flag argument
    -R<flag> Pass <flag> to the remote runtime system.
                            Use one -R for each remote flag or flag argument
...
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