We get people confused by Portage's "masked by: ~amd64 keyword" quite often. The use/terminology here is correct, as "masked by" just means "not visible (because of)", but it's hard to explain that nuance to new users. They often end up reading something is "masked" (meaning p.masked) and then get confused when they see the ~amd64 message. bug 949983 is one example but this comes up often. To start discussion, maybe "unavailable because:"?
