4.L. Service Foot Faults. During the serve, when the ball is
struck, the server’s feet shall:

4.L.1. Not be outside the imaginary extension (or plane)
of the sideline.
4.L.2. Not be on the wrong side of the
imaginary extension (or plane) of the centerline.
4.L.3. Not touch the court, including the baseline.

4.L. Service Foot Faults. During the serve, when the ball is
struck, the server’s feet shall:

Legislative format showing the changes to the original rule.

4.L.1. Not touch the areabe outside the imaginary extension (or plane)
of the sideline.
4.L.2. Not touch the areabe on the wrong side of the
imaginary extension (or plane) of the centerline.
4.L.3. Not touch the court, including the baseline.

4.M.1. The server serves from the incorrect serving area. During the entire serve, the server cannot cross the imaginary plane that is created by the service area lines and imaginary extensions of the sidelines.

4.L. Service Foot Faults. During the serve, when the ball is
struck, the server’s feet shall:

4.L.1. Not touch the area outside the imaginary extension
of the sideline.
4.L.2. Not touch the area on the wrong side of the
imaginary extension of the centerline.
4.L.3. Not touch the court, including the baseline.

The way the current serving rules 4L read a player can have one foot outside the imaginary sideline or centerline extension, practically being on the wrong side of the imaginary line, and when the player throws the ball up for a volley serve, they lift up the foot that is touching the wrong side of the imaginary extension to strike the ball while only touching the correct side of the service area. This serving technique causes the serving player to have an unfair advantage gaining access to angles at a much higher rate of speed and if perfected it can make it almost impossible for the receiving player to return the serve and defend against the 3rd cross court 3rd shot.

Tennis and table tennis rule are much stricter in that the ball must be struck inside the service area, which is why I suggested a correction to 4M.1 as well.

Singles play service is where the current rules can be exploited the most however in doubles play a server  can exploit the rules so that there is not a cross court service and also the serve is at a much higher rate of speed.