`itemDefaults:{}` specifies an item config used for every item in 
`items:[]`. Individual items are free to set their own values.

<pre class="runnable readonly text 300">
itemDefaults: {
    module: Button,
    handler: 'onButtonClick',
    flex: 1
},
items: [{
    style: { backgroundColor: 'red' },
}, {
    style: { backgroundColor: 'yellow' },
}, {
    style: { backgroundColor: 'lightblue' },
}, {
    module: Label // This is used instead of the default
}]
</pre>