Lane shape meaning

Hi, I am wondering what is the meaning of the shape (eg. "LRL, “LSL”, “LSR”, “RLR” etc.) in lane record? And what is the meaning of ‘radius’ & ‘segment_length’ in arcline_path_3?
Also is there any document (except the tutorial) for the map schema like the one for the dataset? I would like to know more details about how each format is connected with each other and how to interpret the attributes inside those formats?