[4.0] 2b9db41 Rewrite for 4.0 - might still need review

[Per Buer]

commit 2b9db41c981d1218c1a83e9b6e6174fe3513f671
Author: Per Buer <perbu at varnish-software.com>
Date:   Wed Feb 26 12:29:27 2014 +0100

    Rewrite for 4.0 - might still need review

diff --git a/doc/sphinx/users-guide/vcl-syntax.rst b/doc/sphinx/users-guide/vcl-syntax.rst
index 14e07ed..15b6da3 100644
--- a/doc/sphinx/users-guide/vcl-syntax.rst
+++ b/doc/sphinx/users-guide/vcl-syntax.rst
@@ -95,4 +95,5 @@ To call a subroutine, use the call keyword followed by the subroutine's name:
 call pipe_if_local;
 
 Varnish has quite a few built in subroutines that are called for each
-transaction as it flows through Varnish. See :ref:`vcl-built-in-subs`.
+transaction as it flows through Varnish. These builtin subroutines are all named vcl_*. Your own subroutines cannot start their name with vcl_.
+See :ref:`vcl-built-in-subs`.