regex_revalidate: optionally retain rule epoch state across restarts

doc/admin-guide/plugins/regex_revalidate.en.rst

@@ -70,6 +70,18 @@ config file changes are checked are only when ``traffic_ctl config reload`` is r
 
     regex_revalidate.so -d -c <path to rules> -l <path to log>
 
+The configuration parameter `--state-file` or `-f` may be used to configure
+the plugin to maintain a state file with the last loaded configuration.
+Normally when ATS restarts the epoch times of all rules are reset to
+the first config file load time which will cause all matching assets to
+issue new IMS requests to their parents for mathing rules.
+
+This option allows the revalidate rule "epoch" times to be retained between ATS
+restarts.  This state file by default is placed in var/trafficserver/<filename>
+but an absolute path may be specified as well. Syntax is as follows::
+
+    regex_revalidate.so -d -c <path to rules> -f <path to state file>
+
 
 Revalidation Rules
 ==================
@@ -127,6 +139,14 @@ currently lead to that rule being removed from the running plugin. In these
 cases, if the rule must be taken out of service, a service restart may be
 necessary.
 
+State File
+----------
+
+The state file is not meant to be edited but is of the format::
+
+<regular expression> <rule epoch> <rule expiry> <type>
+
+
 Examples
 ========