It's documented here... http://www.digitalmars.com/d/2.0/phobos/std_cover.html
... but I can't find it in the Phobos source. (Also, I can't import it -- which is perhaps the most pressing issue :)
It's just that I'm using rdmd (for convenience), but then I don't know where any coverage reports end up (unless I examine the path to the generated executable), so I thought I'd specify where I wanted them...
-- Magnus Lie Hetland http://hetland.org