In reply to Lukasz.

To avoid any confusion and provide more details, the code is actually a mashup of 3 codebases: mostly my own accessibility ready code framework I'm constantly improving over the years, Justin's Mythic and WP Rig. So, this is not specifically a Mythic code, nor a WP Rig code. It really is a custom mashup. (To complicate thing more, my previous code was based on Underscores starter theme too, so I guess you can still find that one in there too :) )

I studied Mythic and WP Rig couple of years ago when I was moving towards modern PHP7+ object oriented programming only.

So, for any code modifications, it's the best to ask for help at support forum.

The theme also uses Theme Hook Alliance action hooks (as all of my themes do).

And you are correct, the theme is indeed speed and SEO optimized, accessibility ready and fully extendable and modifiable.