I'd also like to document some of its fields, but I don't know
what they are.

Change-Id: I87d341e255f785d351a8a73e645be668e02b2689
Reviewed-on: https://go-review.googlesource.com/27399Reviewed-by: David Crawshaw <crawshaw@golang.org>
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>