Snake's Swiftness and "any extra attack"

[Segev]

Snake's Swiftness grants its target an immediate attack which doesn't change init order. It specifically states that anybody who's already taken an extra attack from any source can't benefit from this one, and lists haste as an explicit example. I think it also references itself (so it can't stack with itself or its Mass version).

I would assume that the Speed enhancement on an item would similarly count, since that explicitly doesn't stack with Haste.

But is that the limit of the restriction? Haste-like effects? Or do the attacks granted by TWF/GTWF/MWF/etc. count as "extra" for this purpose? What about attacks granted by having a natural attack routine rather than using BAB?


As further discussion fodder, to what uses might this spell be put in an optimization sense? How badly can it be abused? Or is its restriction sufficient to keep it only so-so?

[Flickerdart]

Unlike most bonus attack givers (which specify they don't stack only with similar haste-like effects) Snake's Swiftness forbids any additional attack at all. Unfortunately, "additional attack" is never defined. BAB iteratives are "gained" but not additional or extra or anything, so they're fine. TWF attacks are "extra" but then so is Haste. Ultimately, it boils down to "the designers didn't think it through and "additional attack" means nothing without DM intervention."