[master] 132a0d0 Document current behavior for bans on non-existing fields

[Nils Goroll]

commit 132a0d0685a1fd9a5a3e36ca6fd8f051a84b8f7d
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Mon Jun 26 19:02:17 2017 +0200

    Document current behavior for bans on non-existing fields

diff --git a/doc/sphinx/reference/vcl.rst b/doc/sphinx/reference/vcl.rst
index 075c345..cb50b6e 100644
--- a/doc/sphinx/reference/vcl.rst
+++ b/doc/sphinx/reference/vcl.rst
@@ -428,6 +428,11 @@ ban(STRING)
   Expressions can be chained using the *and* operator ``&&``. For *or*
   semantics, use several bans.
 
+  The unset *<field>* is not equal to any string, such that, for a
+  non-existing header, the operators ``==`` and ``~`` always evaluate
+  as false, while the operators ``!=`` and ``!~`` always evaluate as
+  true, respectively, for any value of *<arg>*.
+
 hash_data(input)
 ~~~~~~~~~~~~~~~~