ssKey is a _global object that contains properties whose values represent possible key codes returned by a standard keyboard. The numeric values of these key codes can be used when you have to specify a key parameter to one of the Keyboard functions.
When using ssCore.Keyboard.sendKey to send a keystroke to another window you have to specify the virtual keycode of the key you want to send. You can use sscore.KeyBoard.setNotify and the onKey notification to experimentally determine the code for the key you want to send or you can use the properties of ssKey object. For example, to send the letter A you need to know that the virtual key code for "A" is 65, but it's much easier to use ssKey.VK_A instead.