Index: /trunk/src/org/openstreetmap/josm/gui/MainApplication.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/MainApplication.java	(revision 16429)
+++ /trunk/src/org/openstreetmap/josm/gui/MainApplication.java	(revision 16430)
@@ -652,5 +652,9 @@
                 "\t--debug                                   "+tr("Print debugging messages to console")+"\n\n"+
                 "\t--skip-plugins                            "+tr("Skip loading plugins")+"\n\n"+
-                "\t--offline=<osm_api|josm_website|certificates|all> "+tr("Disable access to the given resource(s), separated by comma")+"\n\n"+
+                "\t--offline=" + Arrays.stream(OnlineResource.values()).map(OnlineResource::name).collect(
+                        Collectors.joining("|", "<", ">")) + "\n" +
+                "\t                                          "+tr("Disable access to the given resource(s), separated by comma") + "\n" +
+                "\t                                          "+Arrays.stream(OnlineResource.values()).map(OnlineResource::getLocName).collect(
+                        Collectors.joining("|", "<", ">")) + "\n\n" +
                 tr("options provided as Java system properties")+":\n"+
                 align("\t-Djosm.dir.name=JOSM") + tr("Change the JOSM directory name") + "\n\n" +
Index: /trunk/src/org/openstreetmap/josm/io/CachedFile.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/io/CachedFile.java	(revision 16429)
+++ /trunk/src/org/openstreetmap/josm/io/CachedFile.java	(revision 16430)
@@ -449,4 +449,7 @@
                 if (offline || age < maxAgeMillis) {
                     return localFile;
+                } else if (NetworkManager.isOffline(OnlineResource.CACHE_UPDATES)) {
+                    Logging.warn(OfflineAccessException.forResource(tr("Cache update for {0}", urlStr)).getMessage());
+                    return localFile;
                 }
                 if (cachingStrategy == CachingStrategy.IfModifiedSince) {
Index: /trunk/src/org/openstreetmap/josm/io/OnlineResource.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/io/OnlineResource.java	(revision 16429)
+++ /trunk/src/org/openstreetmap/josm/io/OnlineResource.java	(revision 16430)
@@ -19,4 +19,6 @@
     /** The JOSM website, used for startup page, imagery/presets/styles/rules entries, help, etc. */
     JOSM_WEBSITE(tr("JOSM website")),
+    /** Updates of {@link CachedFile} */
+    CACHE_UPDATES(tr("Cache updates")),
     /** Various government certificates downloaded on Windows to make https imagery work in some countries */
     CERTIFICATES(tr("Certificates")),