Ah, thought you meant something else. This is an odd one-- not sure what the right thing to do is. We have
1. Subcommands that are Runnable (listed in main section).
2. Subcommands that won't be Runnable, but should be listed in the main section.
3. Subcommands that are Runnable or not, but should be listed in the additional topics section.
4. Subcommands that shouldn't be listed at all, but should still be accessible.

Right now, this Unlisted flag differentiates between (1+2 and 3). Not sure 4 is necessary.

Perhaps the right solution is an enum choosing between {commands section, help section, unlisted}, and leave Runnable entirely out of it.