Mission editor command reference and auto complete.

When you are typing a command in an init or other lines in the editor, you will see a brief syntax hint as it tries to complete the word. e.g. type in createVeh and you see a pop-up:

createVehicle [type, position, markers, placement, special]
type createVehicle pos

If that wasn't enough for you, just press F1 when you can see a popup to see the complete comref for that command. Looking at the comref page, you can even press a button to copy the example code to the clipboard so you can paste it directly back into the init or other line you were on.