diff --git a/runtime/doc/testing.txt b/runtime/doc/testing.txt
index 97faea0..362f2b9 100644
--- a/runtime/doc/testing.txt
+++ b/runtime/doc/testing.txt
@@ -1,4 +1,4 @@
-*testing.txt*	For Vim version 9.0.  Last change: 2023 May 04
+*testing.txt*	For Vim version 9.0.  Last change: 2023 May 18
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -166,15 +166,17 @@
 		  Set or drag the left, right or horizontal scrollbar.  Only
 		  works when the scrollbar actually exists.  The supported
 		  items in {args} are:
-		    which:	scrollbar. The supported values are:
+		    which:	Selects the scrollbar. The supported values
+				are:
 				    left  Left scrollbar of the current window
 				    right Right scrollbar of the current window
 				    hor   Horizontal scrollbar
-		    value:	amount to scroll.  For the vertical scrollbars
-				the value can be 1 to the line-count of the
-				buffer.  For the horizontal scrollbar the
-				value can be between 1 and the maximum line
-				length, assuming 'wrap' is not set.
+		    value:	Amount to scroll.  For the vertical scrollbars
+				the value can be between 0 to the line-count
+				of the buffer minus one.  For the horizontal
+				scrollbar the value can be between 1 and the
+				maximum line length, assuming 'wrap' is not
+				set.
 		    dragging:	1 to drag the scrollbar and 0 to click in the
 				scrollbar.