To allow 'Create Masked Layer from Selection' in the Colour Editor to create a new mask within the confines of the mask that the tool was used in

If you wanted to edit the colours within a local area of a frame, while leaving the same colours elsewhere in the frame as they are, it would be useful to isolate the specific part by applying a mask to that area, and then within that localised mask, further isolate your selection with the precision that the Advanced Colour Editor gives you, and create a mask from that selection within the confines of the mask that you made the colour selection.

This way, the same colours will not be unwantingly selected in other parts of the image.