The 'commands' property of both AppBar and Menu can take both a single command or an array of commands. Since there is no syntax to type this duality, we should indicate an array of commands instead.

winjs/winjs.d.ts

@@ -3598,7 +3598,7 @@ declare module WinJS.UI {
 		/**
 		 * Sets the AppBarCommand objects that appear in the app bar.
 		**/
-		commands: AppBarCommand;
+		commands: AppBarCommand[];
 
 		/**
 		 * Gets or sets a value that indicates whether the AppBar is disabled.
@@ -5598,7 +5598,7 @@ declare module WinJS.UI {
 		/**
 		 * Sets the MenuCommand objects that appear in the menu.
 		**/
-		commands: MenuCommand;
+		commands: MenuCommand[];
 
 		/**
 		 * Gets the DOM element that hosts the Menu.