I haven’t explicitly mentioned it in the article, but `srcset` + `sizes` is a way to provide dynamic densities for one image format, then multiply that with one `<source>` for each image format:

    <picture>
      <source srcset='…' sizes='…' type='image/avif'>
      <source srcset='…' sizes='…' type='image/webp'>
      <img srcset='…' sizes='…'>
    </picture>

If this is what you mean, maybe it would be better to include in the article?