🧒 Explain like I'm 5
Imagine your browser is a painter trying to paint a wall. A render-blocking resource is like a delivery that the painter refuses to start without — even if the delivery has nothing to do with painting the first section of the wall. CSS and JS files loaded in the `<head>` are like mandatory deliveries. Using `defer` is like telling the painter 'you can start while the delivery is on its way — just don't use it until it arrives.' Using `async` is even more relaxed: 'use it the second it arrives, even if you're mid-stroke'.
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