Since I happen to have the book handy, will I do for a quote?
1-2-2 If, on an unofficial court, there is less than 3 feet of unobstructed space outside any sideline or end line, a narrow broken line shall be marked on the court parallel with and 3 feet inside that boundary. This restraining line becomes the boundary line during a throw-in on that side or end, as in 7-6. It continues to be the boundary until the ball crosses the line.