pub const HELP_LONG_KEY: u64 = u64::MAX; // 18_446_744_073_709_551_615u64Expand description
The key --help answers to, and the one -h does.
Reserved rather than generated: a derive builds keys from a hash of the type they came from in the high half and an index in the low half, so the top of the range belongs to nobody. Generated code compares against these to tell a help request from a flag of its own.