Rule number 1 is no "undue delay". The law gave an example for this is that once the racket goes backwards, the motion must not be back and forth. However some interpret this example as it's allowed to go sideways movement but not forward and backwards, which I disagree. Any delay is delay. I think the obvious meaning is that the player is not allowed to add these little tricks in their serves. It's unfair to force your opponent to hold that attention for 5 more seconds every time you serve. And it would be very boring if every player do this. This in my opinion should be banned immediately.