An img with "srcset" and sizes" attributes:

<img sizes="(min-width: 40em) 80vw, 100vw"
srcset="../examples/images/medium.jpg 375w, ../examples/images/large.jpg 480w, ../examples/images/extralarge.jpg 768w" alt="A giant stone face at The Bayon temple in Angkor Thom, Cambodia">

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A giant stone face at The Bayon temple in Angkor Thom, Cambodia