[flexcoders] mx:MenuBar - How to choose or trigger on click

[Wally Kolcz]

I am working on a couple AIR apps that would best be served with a menu bar. 
Problem is, as where I do understand how to make menu items, I cannot figure 
out how to trigger a function or switch a viewstack  when a menu item is 
clicked. 

Lets say I have this:
<mx:MenuBar x="0" y="80" width="100%" id="mainMB" click="menuHandler(event)" 
labelField="@label">
        <mx:XMLList>
            <menuitem label="Practice Tests">
                <menuitem label="Load Test" data="load"/>
                <menuitem label="End Test" data="cancel"/>
            </menuitem>
        </mx:XMLList>
    </mx:MenuBar>

I want to trigger a function when either the load or cancel is selected. How?