Accepting all kind of variables is one thing.We had several discussions in the past about use of variables from other modules and somehow it cannot be solved generally. Maybe this module works with avps only, but others accept any kind of variable that can be from all over.
Being documentation, feel free to add whatever you consider it will help, but I don't think there has to be a bug report -- think that some module parameter accepts r/w variables such as avp, sht, memcache, redis, a.s.o., listing all of them will be confusing and I am sure in the future there will be new writable variables from other modules.