Improve Levels tool by visually showing clipping using alt key

When using the levels tool, it's hard to know when the levels are clipping (in each color channel or RGB channel).

Using the Alt/option key (like in PS) showing when the levels are clipping for shadow or highlight input is an efficient way to perfectly and visually know when a color is clipping, or your tree channel "burning".

For exemple: (as used in PS)

If you want to know when your Green channel is clipping:

Shadow: Press alt down when you move your shadow input handle. The image turn tollay green. Moving the shadow handle into the levels and pixels become black when clipping.

Highlight: Press Alt key down when moving your Highlight handle into the Levels. Ima turn totaly black. When pixel start to clip, they become green.

With this method you perfectly know when each pixel start to clip, in each channel, which is useful for pro photographer, photolithographer, precise reprography works, digitization etc.