When it comes to the img tag and the source tags, it simply switches between the first source tag based on the parameters provided.
<picture>
<source media="(min-width: 800px)" srcset="https://via.placeholder.com/800x700">
<source media="(min-width: 900px)" srcset="https://via.placeholder.com/900x800">
<source media="(min-width: 1000px)" srcset="https://via.placeholder.com/1000x900">
<img src="https://via.placeholder.com/500x400" alt="">
</picture>