rules is a list of tuples in the form (specificity, selector, style). The intention is to sort purely by specificity, there is no value in considering the selector or the style in the sort. Simply doing `rules.sort()` would have the same behavior as I believe all specificity values are unique, but I think this code better captures the intent to sort by specificity alone.

If you're happy with this I'll add a comment clarifying what is going on.