Ah, I wasn't aware it was the name of a common code golf challenge, I do code golfing myself but apparently not enough :)

I guess it makes sense people would frame the game that way, arbitrary bit flips seems way too hard, I'm not even sure it's possible for a program to cope on it's own.

To be fair, "radiation" suggests only bit flips.

So by "character mutation" you mean the deletion of characters? Because to my ears that term still sounds like bit flips, i.e. changing characters.

> This tag is for challenges which require answers to still work when a random edit to the source code is made.

What if my random edit is to add a character?

Possible -- depends on the rules of the specific challenge. Most of the time it's edits, deletes, or some combination. Sometimes the score depends on how many edits your code can withstand.