If we look at the word "hyperlinking" it just means the online link has countless ways to connect and be connected to. That also means, it can be linked in a lot of ways simultaneously, within an article, across articles, and beyond. "Discrete texts" means a distinct body of words that make up an article, so it can also be regarded as the originator and target at the same time. The author is trying to use "within, across, between etc." to describe the very intricate network the internet is, with all the various complex connections that a hyperlink can take on. Kinda like saying how I would cross a lane to get to my destination. It can be across the road (by using a traffic crossing), over the road (via a bridge), under the road (through a tunnel) etc.