It will select the first supported format, webp in the example below. <picture> <source srcset="foo.webp" type="image/webp"> <source srcset="foo.jxr"

It will select the first supported format, webp in the example below. <picture> <source srcset="foo.webp" type="image/webp"> <source srcset="foo.jxr" type="image/vnd.ms-photo"> <img src="foo.jpg" alt="" width="100" height="150"> </picture> https://html.spec.whatwg.org/dev/images.html#image-format-based-selection https://html.spec.whatwg.org/dev/images.html#image-format-ba... --- About the Accept header, currently they include `image/avif` so I have no reason to believe that `image/jxl` won't be added.