How to specify an access key for a menu item?

```
            <ContextMenu>
                <MenuItem Header="Copy" Command="Copy" />

```

Per <http://msdn.microsoft.com/en-us/library/windows/desktop/bb545460.aspx#accessKeys>

Edit: I really mean [menu *access keys*](http://msdn.microsoft.com/en-us/library/windows/desktop/bb545460.aspx#menu), not shortcut keys.