Lane splitting is not in the DMV handbook but Lane Sharing is.
Dwight is correct in saying that the drivers move over for you- most of the time!
I used to travel from work (San Onofre Nuclear Generating Station) down I-5 from San Clemente to Oceanside and there is only 3 off ramps in 18 miles. One lets you pull off into a view point overlooking the Pacific Ocean and the 2nd one is at Las Pulgas where the entry to Camp Pendleton is and the 3rd is a rest stop. Many times it would be backed up for 5 miles due to an accident. As long as you don't blast past the cars and scare the drivers there's no trouble. When they are crawling along and we can do 30 mph between them the cars don't have enough time or space to "cut you off". Some people do "drift" over to try and block you but then you just go round the opposite side of them. It can be nerve wracking
"sharing the lane" but you have to be focused while doing it. When doing it for a long time you start to pick up your speed and its real easy to reach 50mph and the cars are only doing 10mph so you have to rein it in a bit. I've had a driver cut me off on a surface street and i ended up brushing into a construction cone. Thats the worst instance for me and all was ok. I hope there are other states that do allow it.
