Shared and GC

[via Digitalmars-d-learn]

I am trying to understand the idea behind "shared" typing fully.

If I am only allowed to share objects with another thread if it 
is typed "shared", doesn't that imply that it should be allocated 
as shared too and only be allowed to contain pointers to "shared"?

That would be nice, because then a precise garbage collector 
could choose between local collection scans and global collection 
scans.

Is this the intended semantics for shared?