patch for #777 - adding documentation and stub for getWarningHTML

git-svn-id: http://svn.openlayers.org/trunk/openlayers@3629 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/EventPane.js

@@ -110,7 +110,11 @@ OpenLayers.Layer.EventPane.prototype =
     /**
      * Method: loadWarningMessage
      * If we can't load the map lib, then display an error message to the 
-     * user and tell them where to go for help.
+     *     user and tell them where to go for help.
+     * 
+     *     This function sets up the layout for the warning message. Each 3rd
+     *     party layer must implement its own getWarningHTML() function to 
+     *     provide the actual warning message.
      */
     loadWarningMessage:function() {
 
@@ -141,6 +145,18 @@ OpenLayers.Layer.EventPane.prototype =
         this.div.appendChild(div);
     },
   
+    /** 
+     * Method: getWarningHTML
+     * To be implemented by subclasses.
+     * 
+     * Return:
+     * {String} String with information on why layer is broken, how to get
+     *          it working.
+     */
+    getWarningHTML:function() {
+        //should be implemented by subclasses
+        return "";
+    },
   
     /**
      * Method: display