Simple way to check which btn is the selected one

hi folks,
again trying to code mcs as buttons in a menu bar, i need specific help with the code below:

btnIdent05.addEventListener(MouseEvent.ROLL_OVER, onRollOverHandler);
function onRollOverHandler(myEvent:MouseEvent){
    // check if this button is selected: HOW TO ???

how to check if the btn is the selected one (to prevent it from behaving as if it wasn’t, ex going to the out state in OVER and OUT) ?

many thanks!