--- srfi-modules.texi.~1.16.~	2003-05-24 09:42:30.000000000 +1000
+++ srfi-modules.texi	2003-06-05 01:45:02.000000000 +1000
@@ -1803,6 +1803,9 @@
 Return the string @var{s1}, but with the characters
 @var{start1} @dots{} @var{end1} replaced by the characters
 @var{start2} @dots{} @var{end2} from @var{s2}.
+
+For reference, note that SRFI-13 specifies @var{start1} and @var{end1}
+as mandatory, but in Guile they are optional.
 @end deffn
 
 @deffn {Scheme Procedure} string-tokenize s [token-set start end]