Like clipping and masking, filters have long been the domain of graphic editors. For example if you wanted to change the saturation of an image, you’d open an editor, make the changes, save the image, and be on your way. Before too long we’ll skip the graphic editor and filter our images through css alone.
Being able to control the transparency of design elements is something we’ve been able to do with css for a few years. However, I often see questions from people, particularly in regards to the opacity property and how child elements inherit opacity from parent elements, which typically isn’t desired.