There should be a option in the bitmap editor (scratch) that allows it to also…….
Just look at this grid example:
000000
045660
056450
064540
000000
If I set my fill color to 9 (white) and click on the center square and change the {insert name here} value thing (like how you can adjust the eraser size in the vector editor) to lets say 2? I would get
000000
099990
099990
099990
000000
Instead of what I get with the {insert name here} at 0 (default fill tool behavior)
000000
045660
059450
064540
000000
Which only fills a single color in… or region, ex:
03
33
Fill tool on bottom square with the color of 9
09
99
I tried very hard to explain this.

If there is anyone who can find a much better way to explain this, please do.