How does GC.addRange work?

[Gary Willoughby via Digitalmars-d-learn]

How does GC.addRange work? i.e. what is it doing? I'm assuming 
reading the docs that it adds a range for the GC to scan but what 
actually happens? Does the GC look into this range and check for 
the existence of pointers it's currently managing?

For example, if i nulled a pointer in the range i added would 
that trigger the GC to collect that resource on the next sweep? 
(assuming it was the last reference.)