What does auto std.stdio.File.ByChunkImpl byChunk (ulong chunkSize ); mean?

[Alex]

On Friday, 3 August 2018 at 16:58:26 UTC, kdevel wrote:
> What does
>
>   auto std.stdio.File.ByChunkImpl byChunk (
>      ulong chunkSize
>   );
>
> on https://dlang.org/library/std/stdio/file.by_chunk.html mean? 
> Is that
> a (forward) declaration of a function named byChunk taking a 
> single
> ulong argument name chunkSize. But what does that function 
> return?

The help page you cited says:
"Returns an input range set up to read from the file handle a 
chunk at a time."