yes blend_screen is a function, unreal has some pretty cool functions made by epic
you can make your own, but they have some already working, and I think if I change one of them I can’t get it back the way it was, so I guess its better to make a copy of it when working on, because you would lose these cool functions.
you could use it in many materials, but if you change the original all of them gonna change so you have to make copies of it to use or you will lose the original, I didn’t use them before today so I’m not sure if you would be able to find it again somewhere, and they save time (like I said there are some really cool ones)
there are two types of nodes to build your shaders Expressions and functions the expressions you can use them over and over again and they don’t carry the changes, but looks like if you change a function you won’t be able to get it back the way it was so I guess they should be used only as examples.
I haven’t being able to find out if I can actually reset them somehow or if there is a library with them somewhere inside unreal.
edit: by the way the material nodes work different inside of a function so functions are not just a material example.