When you access the page, you will see the DOM parent-child relationships 'Parent', 'Child (CHILD)', and 'Grandchild (GRAND CHILD)', of which the first grandchild (orange) is targeted for the event.
Way back in the Blazor 0.1 days events were extremely limited; we had to make do with only three: onclick, onchange and onkeypress. The event data available was also rather basic -- in fact I'm not ...