code: public void setElevation(float elevation) {
          if (drawableState.elevation != elevation) {
              drawableState.shadowCompatRadius = Math.round(elevation);
              drawableState.elevation = elevation;
              invalidateSelfIgnoreShape();
          }
      }
docs: Sets the elevation used to render shadows when {@link #requiresCompatShadow()} is true. This
  value is the same as the native elevation that would be used to render shadows on API 21 and
  up.
  
  <p>TODO: The shadow radius should be the actual radius drawn, elevation should be
  the height of the closest equivalent native elevation which produces a similar shadow.