When it says "giving you the benefits of tools like LESS and Sass" I think they are referring to how you can postprocess the CSS generate by LESS and Sass
Hmm... I can't quite see how the sentence could be parsed that way.
But even if that is the case, it doesn't make any sense to me, and I can't begin to understand how they could be compatible with each other. How are you going to write "var(...)" or "color(...)" declarations within LESS, that LESS will ignore, just to "pass through" to Myth? And why would you? As far as I can tell, Myth doesn't do anything that LESS doesn't already do, so I don't see why anyone would add Myth on top of LESS.
But even if that is the case, it doesn't make any sense to me, and I can't begin to understand how they could be compatible with each other. How are you going to write "var(...)" or "color(...)" declarations within LESS, that LESS will ignore, just to "pass through" to Myth? And why would you? As far as I can tell, Myth doesn't do anything that LESS doesn't already do, so I don't see why anyone would add Myth on top of LESS.