Type Alias Decoding 

pub type Decoding<'a, T> = Pin<Box<dyn Future<Output = T> + 'a>>;

Decoding is an answer a decoder is still working on.

Every answer here is a future because a browser hands back a promise for everything it decodes; a decoder that already has its answer returns std::future::ready, which costs one poll. The future is made and driven on the thread that owns the decoder and never leaves it, so it carries no Send bound.

Aliased Type

#[repr(transparent)]
pub struct Decoding<'a, T> { /* private fields */ }