We have a few tags that are effectively sub-tags, using a prefix and another word. [sr4.shadowrun], [sr4.matrix], and [sr4.technomancer] appear to use that model. I think [dd-oriental-adventures] is using dd as a prefix to "oriental-adventures" but it's difficult to say - it might just be an attempt to prevent ambiguous interpretation. [dice] and [dice-notation] is close, too.
Should we use tags like this? Should we attempt to encourage their use? Is there a better metric than "do it when it seems to make sense" to determine when their use is appropriate?