ARC: add optional x= tag to signing

[exim.git] / doc / doc-txt / experimental-spec.txt

diff --git a/doc/doc-txt/experimental-spec.txt b/doc/doc-txt/experimental-spec.txt
index 3c348d0df6118784c46b3a3677f8ed5fe4eab0c8..b981f3b7a439225668971cfeb3f34a2c669bbca2 100644 (file)
--- a/doc/doc-txt/experimental-spec.txt
+++ b/doc/doc-txt/experimental-spec.txt
@@ -806,9 +806,15 @@ Expanded as a whole; if unset, empty or forced-failure then no signing is done.
 If it is set, all three elements must be non-empty.
 
 The fourth element is optional, and if present consists of a comma-separated list
-of options.  The only option implemented so far is
-  timestamps    Add a t= tag to the generated AMS and AS headers, with the
-                current time.
+of options.  The options implemented are
+
+  timestamps           Add a t= tag to the generated AMS and AS headers, with the
+                       current time.
+  expire[=<val>]       Add an x= tag to the generated AMS header, with an expiry time.
+                       If the value <val> is an plain number it is used unchanged.
+                       If it starts with a '+' then the following number is added
+                       to the current time, as an offset in seconds.
+                       If a value is not given it defaults to a one month offset.
 
 [As of writing, gmail insist that a t= tag on the AS is mandatory]