fix docs

txexpr/scribblings/txexpr.scrbl

@@ -1,6 +1,9 @@
 #lang scribble/manual
 
-@(require scribble/eval (for-label racket txexpr xml (only-in typed/racket require/typed)))
+@; for documentation purposes, use the xexpr? from xml.
+@; the one in txexpr is just to patch over an issue with
+@; `valid-char?` in Racket 6.
+@(require scribble/eval (for-label racket (except-in txexpr xexpr?) xml (only-in typed/racket require/typed)))
 
 @(define my-eval (make-base-eval))
 @(my-eval `(require txexpr xml))