"Guard fields control a reader's experience of the text based on where they have been." #readingtoday  

Guard fields control a reader's experience of the text based on where they have been. This is done by placing conditions on the activation of links, "preventing a link from being followed unless a specific node has been visited". The reader's experience is thus literally as well as metaphorically shaped by the path already taken, enabling Joyce to repeat terms and nodes throughout the work and have them reappear in new contexts. Conversely, they enable Joyce to ensure that readers don't access key nodes until they have seen or visited others; although the narrative seems to be following a path that may have been followed before, it changes slightly at the next turn.