----------
Animated textures do work, but in a buggy way. Having a multi-layer material with one animated texture will result in either no layer moving or all layers moving, based on position of the animated layer.
And texture masking is the technique of making only a certain part of a texture affected by texture manipulation.
Imagine you want to paint letters on the wall, but you have only a spray can, so what do you do? You cover the wall with a plate that has letters for holes, and you spray over that plate to get letters on wall, and paint doesn't touch the parts of the wall that are covered by plate. That's how texture masking works.
----------
Hm I kind of get it but that's a whole new graphical feature for a rather small gain I think..