/// A MIDI Show Control command.
/// Used by [`UniversalRealTimeMsg::ShowControl`](crate::UniversalRealTimeMsg::ShowControl).
///
/// Unimplemented, though the `Unimplemented` value can be used to
/// represent the commands not supported here.
///
/// As defined in MIDI Show Control 1.1.1 (RP002/RP014)