adding comment for dealing with popups and layers

git-svn-id: http://svn.openlayers.org/trunk/openlayers@577 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Map.js

@@ -144,7 +144,28 @@ OpenLayers.Map.prototype = {
         this.events.triggerEvent("addlayer");
     },
 
-    /**
+    /** Removes a layer from the map by removing its visual element (the 
+     *   layer.div property), then removing it from the map's internal list 
+     *   of layers, setting the layer's map property to null. 
+     * 
+     *   a "removelayer" event is triggered.
+     * 
+     *   very worthy of mention is that simply removing a layer from a map
+     *   will not cause the removal of any popups which may have been created
+     *   by the layer. this is due to the fact that it was decided at some
+     *   point that popups would not belong to layers. thus there is no way 
+     *   for us to know here to which layer the popup belongs.
+     *    
+     *     A simple solution to this is simply to call destroy() on the layer.
+     *     the default OpenLayers.Layer class's destroy() function
+     *     automatically takes care to remove itself from whatever map it has
+     *     been attached to. 
+     * 
+     *     The correct solution is for the layer itself to register an 
+     *     event-handler on "removelayer" and when it is called, if it 
+     *     recognizes itself as the layer being removed, then it cycles through
+     *     its own personal list of popups, removing them from the map.
+     * 
      * @param {OpenLayers.Layer} layer
      */
     removeLayer: function(layer) {