Add list of supported time zone IDs, rephrase some of the doc

core/src/main/java/hudson/scheduler/CronTabList.java

@@ -110,7 +110,7 @@ public final class CronTabList {
                 if(timezone != null) {
                     LOGGER.log(Level.CONFIG, "CRON with timezone {0}", timezone);
                 } else {
-                    throw new ANTLRException("Invalid or unsupported timezone '" + line + "'");
+                    throw new ANTLRException("Invalid or unsupported timezone '" + timezone + "'");
                 }
                 continue;
             }

core/src/main/resources/hudson/triggers/TimerTrigger/help-spec.html → core/src/main/resources/hudson/triggers/TimerTrigger/help-spec.jelly

+<?jelly escape-by-default='true'?>
+<j:jelly xmlns:j="jelly:core" xmlns:l="/lib/layout">
 <div>
   This field follows the syntax of cron (with minor differences).
   Specifically, each line consists of 5 fields separated by TAB or whitespace:
@@ -80,31 +82,33 @@ H H(9-16)/2 * * 1-5
 # once a day on the 1st and 15th of every month except December
 H H 1,15 1-11 *
 </pre>
+<h3>Timezone specification</h3>
+<j:invokeStatic className="java.util.TimeZone" method="getDefault" var="currentTimeZone"/>
 <p>
-  <b>Timezone specification</b>. <br/>
   Periodic tasks are normally executed at the scheduled time in the timezone of 
-  the Jenkins master JVM (currently Central European Time). 
-  This behaviour can be <b>optionally</b> changed by specifying an alternative timezone in the
+  the Jenkins master JVM (currently <strong>${currentTimeZone.getID()}</strong>).
+  This behavior can optionally be changed by specifying an alternative timezone in the
   first line of the field.
+  Timezone specification starts with <code>TZ=</code>, followed by the ID of a time zone.
 </p>
-<ul>
-  <li>Timezone specification should contain the &quot;TZ=$(timezoneID)&quot; string</li>
-  <li>If a timezone is not specified, the default Jenkins JVM timezone will be used</li>
-  <li>Th supports all timezones returned by 
-    <a href="https://docs.oracle.com/javase/7/docs/api/java/util/TimeZone.html#getAvailableIDs()">
-      java.util.TimeZone::getAvailableIDs()
-    </a> on the Jenkins server JVM
-  </li>
-  <li>Examples: EST, Etc/GMT+5, US/Pacific, America/Indiana/Petersburg, etc.</li>
-</ul>
+  <p>
+    Complete example of a schedule with a timezone specification:
+  </p>
+  <pre>
+    TZ=Europe/London
+    # This job needs to be run in the morning, London time
+    H 8 * * *
+    # Butlers do not have a five o'clock, so we run the job again
+    H(0-30) 17 * * *
+  </pre>
 <p>
-  Example:
+  The supported timezones depend on the Java runtime Jenkins is running on. The list of supported time zone IDs on this instance is:
 </p>
-<pre>
-TZ=Europe/London
-# This job needs to be run in the morning, London time
-H 8 * * *
-# Butlers do not have a five o'clock, so we run the job again
-H(0-30) 17 * * * 
-</pre>
+<j:invokeStatic className="java.util.TimeZone" method="getAvailableIDs" var="timeZones"/>
+<ul>
+  <j:forEach items="${timeZones}" var="timeZone">
+    <li>${timeZone}</li>
+  </j:forEach>
+</ul>
 </div>
+</j:jelly>
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