Macro frame_support::impl_outer_dispatch

macro_rules! impl_outer_dispatch {
    (
		$(#[$attr:meta])*
		pub enum $call_type:ident for $runtime:ident where origin: $origin:ty {
			$(
				$( #[codec(index = $index:tt)] )? $module:ident::$camelcase:ident,
			)*
		}
	) => { ... };
    (@DISPATCH_MATCH
		$self:ident
		$call_type:ident
		$origin:ident
		{ $( $generated:tt )* }
		$index:expr;
		$name:ident
		$( , $rest:ident )*
	) => { ... };
    (@DISPATCH_MATCH
		$self:ident
		$call_type:ident
		$origin:ident
		{ $( $generated:tt )* }
		$index:expr;
	) => { ... };
}

Implement a meta-dispatch module to dispatch to other dispatchers.