A pattern that is used to recognize a list header. This is used for the "n" flag in 'formatoptions'. The pattern must match exactly the text that will be the indent for the line below it. You can use |/\ze| to mark the end of the match while still checking more characters. There must be a character following the pattern, when it matches the whole line it is handled like there is no match. The default recognizes a number, followed by an optional punctuation character and white space.