Index: io.c
===================================================================
--- io.c	(revision 26044)
+++ io.c	(working copy)
@@ -1133,6 +1133,8 @@
  *     f.rewind     #=> 0
  *     f.lineno     #=> 0
  *     f.readline   #=> "This is line one\n"
+ * 
+ *  Note that it cannot be used with streams such as pipes, ttys, and sockets.
  */
 
 static VALUE
@@ -1215,8 +1217,10 @@
  *     r, w = IO.pipe
  *     r.eof?  # blocks forever
  *
- *  Note that <code>IO#eof?</code> reads data to a input buffer.
- *  So <code>IO#sysread</code> doesn't work with <code>IO#eof?</code>.
+ *  Note that <code>IO#eof?</code> reads data to the input buffer.
+ *  So <code>IO#sysread</code> only works with <code>IO#eof?</code>
+ *  if you call <code>IO#rewind</code> first (which is not available
+ *  for some streams).
  */
 
 VALUE