other gzip compression methods ?

I am trying to find where in the code controls how cached files are gzip compressed i.e.

```
index.html.gz
```

and whether it's possible to use other compression methods with higher compression ratios like zopfli or higher compression levels ?

at https://github.com/Automattic/wp-super-cache/blob/master/wp-cache-phase1.php#L210 ?