How exactly does Tuple work?

[Jan Hönig]

I have a simple question.
How exactly does Tuple work?

In detail, I am interested in expand and opSlice.

For expand, I have found the line: 
https://github.com/dlang/phobos/blob/master/std/typecons.d#L618

How does that work, where is the rest? What does it do?


Similary I can access tuples with `[0]`.
But there is no opSlice.
It is also not specified in the docu: 
https://dlang.org/phobos/std_typecons.html#Tuple


Last but not least, I can use `length`.
How does that work? Where is it?


I probably don't need an explenation, I mainly need to be pointed 
in the right direction.
So instead of sacrificing your time writing an answer, a link to 
the lines I should look at would be fully suficient.

Thanks in advance!

BR,
Jan