It's known as a PRM approach.
Somewhat doubt it..but anyway when I've been involved in these specifically at SFO one, or more usually both the aircraft involved have been on a visual approach with no magenta line/ILS/breakout frequencies required....
How does this work?
It's not rocket science, it's a use of basic pilot s***, sadly often long forgotten in the rush to codify everything and label it with an acronym. In short ATC say "fella, it's a nice day, look out the window, fly your aircraft accurately and land on your assigned runway, keeping an eye on the guy on your left/right". Simples.....
The slightly more complex answer is as DR has said, down to parallel lines... Usually how it works at SFO if they are landing to the west is that one aircraft flies a right hand traffic pattern, e.g. flying over San Francisco Bay bay for right turns to a visual approach onto 28 Right, the other traffic will fly a left hand traffic pattern coming in from the south for 28 Left (Google earth might help you visualise this if you are not familiar with the geography).
ATC "caution" you about the other traffic then let you get on with it..it's quite entertaining when you are pointing at each other on base leg....above all the really big thing to remember is not to fly through your centreline...
Almost proper flying and it can make for a fun end to a long haul day out....