?
Means Help, Nonprinting Characters, Alphanumeric (in Patterns) or Optional (in Regexp)
Typing a question mark in the Visual home line or in response to the Line mode prompt (/), is a request for on-line Help. In Visual you can get more detailed assistance by typing Help, instead of “?,” in the home line.
When Visual prints a ? at the start of a line, it means that the line contains nonprinting characters, which are replaced by dots (.).
Question mark “?” in patterns matches a single alphabetic or numeric character:
/list "BASE??"(pattern) {“BASE” plus 2 alphanumerics}
A question mark (?) in regular expressions qualifies the preceding character and makes it optional. This means the character may or may not be there. In either case, the search is successful.
/list "cancell?ed" (regexp) {“canceled” and “cancelled” are found}