doc fix: ? is used for quantification

brag/brag/brag.scrbl

@@ -689,8 +689,8 @@ continues till the end of the line.
 A @deftech{multiline comment} begins with @litchar{(*} and ends with @litchar{*)}.
 
 An @deftech{identifier} is a sequence of letters, numbers, or
-characters in the set @racket["-.!$%&/<=>?^_~@"]. It must not contain
-@litchar{*}, @litchar{+}, or @litchar|{{}| and @litchar|{}}|, as those characters are used to denote quantification.
+characters in the set @racket["-.!$%&/<=>^_~@"]. It must not contain
+@litchar{*}, @litchar{+}, @litchar{?}, or @litchar|{{}| and @litchar|{}}|, as those characters are used to denote quantification.
 
 A @deftech{pattern} is one of the following:
 @itemize[