What is RTInfo?

[Mike via Digitalmars-d-learn]

object.d [1] says it's infomation for the precise GC (which I 
thought wasn't implemented yet).

It just seems to return a void*.  But, searching the source code, 
it doesn't seem to be set by anything anywhere.

So, what is RTInfo and what is its purpose.  And how is it 
different from TypeInfo?

Thanks,
Mike

[1] 
https://github.com/D-Programming-Language/druntime/blob/f0c1e13d8bd547eed517b1ae17f085966bb165c1/src/object.di#L180