After pondering the dark wander's answerthe dark wander's answer for a minute or two, I think I'd like to offer up the option that it is completely useless to us as a tag and should be nuked.
If there are to be questions about works sacred to the various sects and faith traditions, they should be tagged with what they are, not using the blanket tag extra-biblical. I don't think there are any sacred works that wouldn't merit their own tag and the existence of a nebulous tag is confusing.