Might want to shoot that idea over to NEI's Dev. Or add it to the "suggest a mod" thread, because I don't think there is a way to do what you ask.
It would be good to have a command that lets you search for a type of item. Like typeing classedas.sword in to NEI would pull up things registered as a sword, or classedas.hat will bring up items that can go in to the head slot. It could even work with baubles.
But I am guessing this would hinge on modders registering their stuff in a standardized predictible manner.
Just say I made a mod that adds a special lazer sword but I used no classes that relate to a sword, because to get what I wanted I had to start from scratch. Id have to know about the NEI function or addon and add support manually. Otherwise it might be classified in the same category as a stick or cooked chicken.
NotEnough resources suffers from this drawback. It labels the drop chance for vannila and thaumcraft easy enough but it doesn't read lycanites mobs data. Probably because Lycanites needs to extend support to it.
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