--- a/browser/base/content/tabcandy/app/groups.js
+++ b/browser/base/content/tabcandy/app/groups.js
@@ -626,20 +626,20 @@ window.Group.prototype = iQ.extend(new I
       if (a.isAnItem) {
         item = a;
         $el = iQ(a.container);  
       } else {
         $el = iQ(a);
         item = Items.item($el);
       }
       
+      Utils.assertThrow('shouldn\'t already be in another group', !item.parent || item.parent == this);
+
       item.removeTrenches();
-      
-      Utils.assert('shouldn\'t already be in another group', !item.parent || item.parent == this);
-  
+        
       if (!dropPos) 
         dropPos = {top:window.innerWidth, left:window.innerHeight};
         
       if (typeof(options) == 'undefined')
         options = {};
         
       var self = this;
       

--- a/browser/base/content/tabcandy/app/items.js
+++ b/browser/base/content/tabcandy/app/items.js
@@ -303,17 +303,17 @@ window.Item.prototype = {
   // Rotates the object to the given number of degrees.
   setRotation: function(degrees) {
     var value = "rotate(%deg)".replace(/%/, degrees);
     iQ(this.container).css({"-moz-transform": value});
   },
     
   // ----------
   // Function: setParent
-  //
+  // Sets the receiver's parent to the given <Item>. 
   setParent: function(parent) {
     this.parent = parent;
     this.removeTrenches();
     this.save();
   },
 
   // ----------  
   // Function: pushAway

--- a/browser/base/content/tabcandy/app/storage.js
+++ b/browser/base/content/tabcandy/app/storage.js
@@ -34,16 +34,18 @@
  * the terms of any one of the MPL, the GPL or the LGPL.
  *
  * ***** END LICENSE BLOCK ***** */
 
 // **********
 // Title: storage.js 
 
 // ##########
+// Class: Storage
+// Singleton for permanent storage of TabCandy data. 
 Storage = {
   GROUP_DATA_IDENTIFIER:  "tabcandy-group",
   GROUPS_DATA_IDENTIFIER: "tabcandy-groups",
   TAB_DATA_IDENTIFIER:    "tabcandy-tab",
   UI_DATA_IDENTIFIER:    "tabcandy-ui",
   VISIBILITY_DATA_IDENTIFIER:    "tabcandy-visibility",
 
   // ----------
@@ -80,23 +82,27 @@ Storage = {
           observer, "browser-delayed-startup-finished", false);
       }
     } catch(e) {
       Utils.log(e);
     }  
   },
 
   // ----------
+  // Function: init
+  // Sets up the object. 
   init: function() {
     this._sessionStore =
       Components.classes["@mozilla.org/browser/sessionstore;1"]
         .getService(Components.interfaces.nsISessionStore);
   },
 
   // ----------
+  // Function: wipe
+  // Cleans out all the stored data, leaving empty objects. 
   wipe: function() {
     try {
       var win = Utils.getCurrentWindow();
       
       var self = this;
       
       // ___ Tabs
       Tabs.forEach(function(tab) {
@@ -111,24 +117,28 @@ Storage = {
       this._sessionStore.setWindowValue(win, this.GROUP_DATA_IDENTIFIER,
         JSON.stringify({}));
     } catch (e) {
       Utils.log("Error in wipe: "+e);
     }
   },
   
   // ----------
+  // Function: saveTab
+  // Saves the data for a single tab. 
   saveTab: function(tab, data) {
     Utils.assert('tab', tab);
 
     this._sessionStore.setTabValue(tab, this.TAB_DATA_IDENTIFIER,
       JSON.stringify(data));
   },
 
   // ----------
+  // Function: getTabData
+  // Returns the data object associated with a single tab.
   getTabData: function(tab) {
     Utils.assert('tab', tab);
 
     var existingData = null;
     try {
 /*         Utils.log("readTabData: " + this._sessionStore.getTabValue(tab, this.TAB_DATA_IDENTIFIER)); */
       var tabData = this._sessionStore.getTabValue(tab, this.TAB_DATA_IDENTIFIER);
       if (tabData != "") {
@@ -139,98 +149,121 @@ Storage = {
       Utils.log(e);
     }
     
 /*     Utils.log('tab', existingData); */
     return existingData;
   },
 
   // ----------
+  // Function: saveGroup
+  // Saves the data for a single group, associated with a specific window. 
   saveGroup: function(win, data) {
     var id = data.id;
     var existingData = this.readGroupData(win);
     existingData[id] = data;
     this._sessionStore.setWindowValue(win, this.GROUP_DATA_IDENTIFIER,
       JSON.stringify(existingData));
   },
 
   // ----------
+  // Function: deleteGroup
+  // Deletes the data for a single group from the given window.
   deleteGroup: function(win, id) {
     var existingData = this.readGroupData(win);
     delete existingData[id];
     this._sessionStore.setWindowValue(win, this.GROUP_DATA_IDENTIFIER,
       JSON.stringify(existingData));
   },
 
   // ----------
+  // Function: readGroupData
+  // Returns the data for all groups associated with the given window.
   readGroupData: function(win) {
     var existingData = {};
     try {
 /*         Utils.log("readGroupData" + this._sessionStore.getWindowValue(win, this.GROUP_DATA_IDENTIFIER)); */
       existingData = JSON.parse(
         this._sessionStore.getWindowValue(win, this.GROUP_DATA_IDENTIFIER)
       );
     } catch (e) {
       // getWindowValue will fail if the property doesn't exist
       Utils.log("Error in readGroupData: "+e);
     }
     return existingData;
   },
 
   // ----------
+  // Function: saveGroupsData
+  // Saves the global data for the <Groups> singleton for the given window.  
   saveGroupsData: function(win, data) {
     this.saveData(win, this.GROUPS_DATA_IDENTIFIER, data);
   },
 
   // ----------
+  // Function: readGroupsData
+  // Reads the global data for the <Groups> singleton for the given window.  
   readGroupsData: function(win) {
     return this.readData(win, this.GROUPS_DATA_IDENTIFIER);
   },
   
   // ----------
+  // Function: saveUIData
+  // Saves the global data for the <UIClass> singleton for the given window.  
   saveUIData: function(win, data) {
     this.saveData(win, this.UI_DATA_IDENTIFIER, data);
   },
 
   // ----------
+  // Function: readUIData
+  // Reads the global data for the <UIClass> singleton for the given window.  
   readUIData: function(win) {
     return this.readData(win, this.UI_DATA_IDENTIFIER);
   },
 
   // ----------
+  // Function: saveVisibilityData
+  // TODO: fold into saveUIData
   saveVisibilityData: function(win, data) {
     this.saveData(win, this.VISIBILITY_DATA_IDENTIFIER, data);
   },
 
   // ----------
+  // Function: readVisibilityData
+  // TODO: fold into readUIData
   readVisibilityData: function(win) {
     return this.readData(win, this.VISIBILITY_DATA_IDENTIFIER);
   },
     
   // ----------
+  // Function: saveData
+  // Generic routine for saving data to a window. 
   saveData: function(win, id, data) {
     try {
       this._sessionStore.setWindowValue(win, id, JSON.stringify(data));
     } catch (e) {
       Utils.log("Error in saveData: "+e);
     }
     
 /*     Utils.log('save data', id, data); */
   },
 
   // ----------
+  // Function: readData
+  // Generic routine for reading data from a window. 
   readData: function(win, id) {
     var existingData = {};
     try {
       var data = this._sessionStore.getWindowValue(win, id);
       if (data)
         existingData = JSON.parse(data);
     } catch (e) {
       Utils.log("Error in readData: "+e);
     }
     
 /*     Utils.log('read data', id, existingData); */
     return existingData;
   }
 };
 
+// ----------
 Storage.init();