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