If you wish to slide an uncontrolled rank, you must first ask your opponent's permission. If granted, you must then slide the rank. If denied, you may not slide the rank that turn, but you may ask again on subsequent turns. You do not need permission to slide a rank you control. You may not slide a rank your opponent controls.
Ranks slide one space to the left or right.
The board can never extend past files a or h. Ranks 2 and 5 are fixed and cannot slide. From the starting position, white could slide rank 1 one space to the white's right.