TIL: https://lukaslueg.github.io/macro_railroad_wasm_demo

It clearly shows that an else can be used solely without a leading `if.
A quick jump into the compiler shows it as well:

use cfg_if::cfg_if;

fn main() { 
    cfg_if! {
        else {
            fn a() {
                println!("Foo");
            }
        }
    }
    a();
}

Is this intended? If yes, it should be documented, if not, it should be prohibited.