Context: "If in Your Dreams; the Flood" is the title of a visual novel. In short, it's story about a girl who suffers from constant nightmares, namely she has dreasm about the flood, and each time she sleeps the flood becomes more dangerous and frightening.
I suspect that ";" meant to show that the visual novel has TWO names, ("If in Your Dreams" and "The Flood" respectively), they were just combined in one title.
Am I correct? If not, then what can it mean?