The advantage of traditional masking using pan film is that you can expose it selectively to given parts
of the spectrum, just like using pan film in a camera with colored filters to alter the values in the scene,
and then can develop it according to the contrast level you wish etc. Something called Minute Mask came along which used photochromic glass like in transition sunglasses, which was exposed by a flash
unit to achieve a generic mask, but the dyes in this product fade over time, and "generic" was about
what to expect from it. And now someone has an industrial product probably to act like a resist
for photochemical etching, but I don't really know much more than that. Masking can either be as simple
or complex as you wish. Once density builds up much, some kind of secondary lith mask is often required prior to the primary pan mask, but this all depends upon the specifics. Beyond that I guess someone could write a book or two about it. Masking color neg film is inherently fussy because it already has an orange contrast mask in place, and every little tweak is like power steering. Plus you have to somehow veer past that orange bias in the first place if you don't want a flat tire. Fortunately,
many images print just fine without supplemental masking. It's those that don't that can test your skill.