Bell
Set Visual Bell 'nnn | "char"
(Default=None)
If you edit text containing Bell characters, they will appear as dots with a "?" at the left of the line. Otherwise, they would disappear from your file when you press Enter because Bells are not saved in display memory. To get around this problem, you can define another character as a translation for the Bell character. For example, Set Vis Bell "|" defines "|" to represent Bell.
When Visual needs to print a Bell on the screen, it prints a "|" instead. When Visual sees any "|" on the screen, it converts it into a Bell internally. To avoid turning every occurrence of the "alias" character in your file into a Bell, Visual prints a "?" for any line with a valid alias already in it and will not let you update that line in Visual mode (use Modify instead).