When I set a flag like this:

app.add_flag("--hidden,!--no-hidden", showHiddenFiles, "Show or hide hidden files");

the resulting help text looks like this:

--hidden, --no-hidden{false}          Show or hide hidden files

It would be nice to have the ability to hide the {false} part. I did not find such an option in the docs/code. Also using a custom formatter doesn't seem to help, since this behaviour is defined in std::string Option::get_name(bool positional, bool all_options).