CURLOPT_RANGE: for HTTP servers, range support is optional

docs/libcurl/opts/CURLOPT_RANGE.3

@@ -5,7 +5,7 @@
 .\" *                            | (__| |_| |  _ <| |___
 .\" *                             \___|\___/|_| \_\_____|
 .\" *
-.\" * Copyright (C) 1998 - 2014, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" * Copyright (C) 1998 - 2015, Daniel Stenberg, <daniel@haxx.se>, et al.
 .\" *
 .\" * This software is licensed as described in the file COPYING, which
 .\" * you should have received as part of this distribution. The terms
@@ -35,9 +35,13 @@ out and X and Y are byte indexes.
 HTTP transfers also support several intervals, separated with commas as in
 \fI"X-Y,N-M"\fP. Using this kind of multiple intervals will cause the HTTP
 server to send the response document in pieces (using standard MIME separation
-techniques). For RTSP, the formatting of a range should follow RFC2326 Section
-12.29. For RTSP, byte ranges are \fBnot\fP permitted. Instead, ranges should
-be given in npt, utc, or smpte formats.
+techniques). Unfortunately, the HTTP standard (RFC 7233 section 3.1) allows
+servers to ignore range requests so even when you set \fICURLOPT_RANGE\fP for
+a request, you may end up getting the full response sent back.
+
+For RTSP, the formatting of a range should follow RFC2326 Section 12.29. For
+RTSP, byte ranges are \fBnot\fP permitted. Instead, ranges should be given in
+npt, utc, or smpte formats.
 
 Pass a NULL to this option to disable the use of ranges.
 .SH DEFAULT