Remember ECMAScript for XML (E4X)? Deprecated in 2014.
https://en.wikipedia.org/wiki/ECMAScript_for_XML

var sales = <sales vendor="John">
<item type="peas" price="4" quantity="6"/>
<item type="carrot" price="3" quantity="10"/>
<item type="chips" price="5" quantity="3"/>
</sales>;

alert( sales.item.(@​type == "carrot").@​quantity );
alert( sales.@​vendor );
for each( var price in sales..@​price ) {
alert( price );
}

@rauschma I guess it's spelt “JSX” nowadays.