Lets talk about fibers

[Suliman via Digitalmars-d]

"The type of concurrency used when logical threads are created is 
determined by the Scheduler selected at initialization time. The 
default behavior is currently to create a new kernel thread per 
call to spawn, but other schedulers are available that multiplex 
fibers across the main thread or use some combination of the two 
approaches" (с) dlang docs

Am I right understand that `concurrency` is just wrapper that 
hide implementation of tasks and fibers? So programmer can work 
with threads like with fibers and vice versa?

If yes, does it's mean that spawns is planing not but with system 
Scheduler, but with DRuntime Scheduler (or how it's can be 
named?) and all of them work in user-space?