What options to work with the release Smooth and Feather in the menu Select -> Modify are different from each other?

I can't surprise the fundamental difference in their work and would very much like to understand it. Please tell me if you can with examples.
July 2nd 19 at 14:19
1 answer
July 2nd 19 at 14:21
Feather — smooths penetrating the object selection.
Smooth — just smooths the corners of the selection.
Clear all will make the procedure the same shapes with the same settings and apply the mask.

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