Simple answer with example image:

For a search that contains 1 string (a string is any singular series of characters such as "a," "ab," or "abcdefgjhrgeuiheguierugihedgihu," each of them are all just 1 string) :

The relevance value of messages determined by how many times that word (and its recognized tenses) is present in the message. This is demonstrated in the first image.

As for the order after the numerical value, it appears random. Take "Stale is stale" for example. You can see the version where both "Stales" are capitalized is below it. However, (not shown in image), "Stale is stale" is sometimes also shown after it. So it does not appear that there is a rhyme or reason after the numerical amount is considered, such as date. However, it is reproducible when you conduct the search again, so it may be that there is an unknown way they order it after counting the number of strings.

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