[plt-scheme] find-snip 'findKind' syntax error message

A question from a novice:

(send ED find-snip 1 '(before-or-none) #f)  ; ED is a text% editor 
containing one image-snip%

-->  find-snip in text%: expects argument of type <findKind symbol>; 
given (before-or-none)

I'm not sure what this means, and I haven't found any reference to 
"findKind" in the Help Desk.

Thanks in advance for any help/advice/pointers.

David