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 playing surface outside the imaginary extension of the sideline.

4.L.2. Not touch the area court on the wrong side of the imaginary extension of the centerline.

4.L.3. Not touch the court, including the baseline or the court inside the baseline.

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.

This change uses the definitions of court and playing surface to define the 'areas' mentioned in the rule.  The change is for clarity purposes.