@andrewdavidloftus go ahead and get into powder toy, pause it, create some photons and try to erase them, go ahead. all other particles can be erased except for photons. that wasn't the point of my original post but it would counter yours. I was using photons as an example because they have ALMOST nothing to do with electricity in PowderToy yet are under the Electronics category.
We were thinking about moving them to radioactive but... Anyway photons, because of glass and refraction, are now graphics, not elements. Therefore, non-erasable.
Hmm... What about a Fundamental category? it would have Black and Whiter hole, Portals, Clone and Void, and what ever other elements directly interacted with the spawning, deletion and moving of particles.
Also perhaps a "Tools" category, it would include air, vacuum, heat, cool, eraser and other non-particle elements
Or we could put peculiar solids like INVS and FILT into the special tab, put cold flame into the explosives tab, put portal and pump into special tab, and put photons into radioactive tab.