If the `$VISUAL` environment variable is set, it will be used as the program to edit the function. If `$VISUAL` is unset but `$EDITOR` is set, that will be used. Otherwise, a built-in editor will be used.
- `-e command` or `--editor command` Open the function body inside the text editor given by the command (for example, "vi"). The command 'fish' will use the built-in editor.
- `-i` or `--interactive` Open function body in the built-in editor.