"A clipping mask is a group of layers to which a mask is applied. The bottommost layer, or base layer, defines the visible boundaries of the entire group. For example, suppose you have a shape in the base layer, a photograph in the layer above it, and text in the topmost layer."
Seems like this should be readily available, but I can't seem to find a way to do it.
Implementations using css, canvas clip, and webgl