Tab
Set Visual Tab [ 'nnn | "char" ]
(Default=None)
If you edit text containing tab characters, most will appear as dots with a “?” at the left of the line. Otherwise the tab characters would be executed by your terminal and be lost. To get around this problem, you can define another character as a translation for the tab character. For example, Set Vis Tab “\” defines “\” as meaning tab.
When Visual needs to print a tab on the screen, it prints a “\” instead. When Visual sees any “\” on the screen, it converts it into a tab internally. To avoid every valid occurrence of an alias character turning into a tab, Visual mode looks for alias characters that already occur in the text. Any line with a valid alias in it is printed with a “?” and Visual will not let you update it (use Modify instead).