Module download 

What a download(…) call can bind, shared by the checker, which reads the call, and everything that runs it.

Enums

DownloadCommand

What code asks of a running download, by its id. repr(u32) because compiled apps pass it to the runtime, which every platform’s C calling convention passes without widening.

DownloadField

A piece of state a download reports into. Compiled apps pass it to the runtime by its code.