Confusion with three sorting options

When it comes to image sorting in searches I understand most of the sorts, but I haven’t figured out how relevance and more recently duration work. I also notice that the random sort doesn’t change every time, so is there just a much more complicated algorithm to that method?

Relevance works with searches that use “OR”, e.g. if you search for “fluttershy || twilight”, relevance will put images with both tags first, then images with only one of the tags. You can also weight tags like this: “fluttershy^2 || twilight”.
 
Duration refers to the duration of videos or gifs.
 
Random is just random, but it uses a seed to determine the randomness. With the same search and same seed, the order will always be the same. This is why you can go back and forth pages on the search results of a random search and get the same images when you go back to the same page. You can see the seed in the address bar of your browser, e.g. “sf=random:4083435784”, where 4083435784 is the seed. You can manually change that, or just open a new page and do another search there.

Thanks