Currently you can add a new entry in the image dab by clicking clipboard. This is good for creating PERMANENT brush dabs.

But it should also be possible to have temporary clipboard dab,that does not create a new entry.
This would have the advantage of constantly updating the clipboard via selecting and copying. Then USING a brush with ACTIVE CLIPBOARD checked on would result in a constantly changing brush dab,when clipboard is changed.

WHY: in animation ,but also in image painting some selected areas can be reused (like faces,hands....) Some applications refer to this as a cutbrush. The advantage is quickly updating image dabs with selections. A bit like COLOR picking,but for images. (=image picking?)

placement in the UI needs to be discussed