Fibers under the hood

[Jonathan Marler via Digitalmars-d-learn]

I've googled and searched through the forums but haven't found 
too much on how fibers are implemented.  How does yield return 
execution to the caller but then resume execution in the same 
place on the next call?  Also some information on how the fiber 
call stack works would be nice.  I'm assuming it allocates the 
stack on the GC heap.  If so, what is the default size and is 
that configurable?  Any information or pointers to resources that 
provide this information would be helpful.  Thanks.