There ya go. Yes, not everything can be done with a single rule

Because then I'd have to have a "EverythingButDark" or "EverythingButWind" and I'm not programming in every possible combination XD
However, if you just want a variable the excludes one element, you could do <if NotPetElement="Fire|Earth|Water|Thunder|Dark|Wind| Ice"> </if> But no, there's no variable specifically to do that.
If you're going to use %PetElement as a variable decider, you have to make variables for all cases, otherwise the effect is undefined. I haven't tried it, but I'd assume it'll just swap in an empty string if it's not found.
Either that or it tries to send /equip hands "$Perp-Fire" as the line (since the variable would never resolve. Either that or /equip hands "-Fire" if it swaps in an empty string in place of unfound variables.
I didn't write that portion of the code, so I'd have to wade through it again to find it.
EDIT: Spoilered the quote... ugh