How to make XML Event ID's in FSX

I Was trying to Learn XML so I can make an Overhead PanelFor a 747-400 in FSX. I was thinking of making the gauge for When like you are at an airport and you are hooked up with a generatorcart and have power applied to the aircraft. The 747 needs 2 cartsand to have power available before you turn the power switch on. I was thinking that if you are parked at a parking spot with a Jetway, thenhave the XML code ask is TOGGLE_JETWAY hooked up true or false like an if then Else statement then have power Available on the Overhead panel.Then Now you have power applied to the Aircraft. First ? // Next How do you use the APU like APU_GENERATOR_SWITCH_TOGGLE Use "No" Aircraft Fuel while operating just like hooked up to a Generator cart on the line with support Equiptment. Also how would you turn on the Hydraulics withouthaving an Engine running Like in real Life, not having it being indexed:to an Engine in FSX. I am just Trying to Learn XML I have good Ideas Except I don't Know How to do! Any Help Would be Greatly Appreciated!