p.boxed.
  The board is divided into 16 square cells of size 2x2.
  A piece must change cell at each move.

p.
  The board is decomposed into 16 little 2x2 squares, starting from
  a1,b1,a2,b2 until g7,h7,g8,h8. When a piece moves, it must cross at least
  one boundary: it cannot remain in the same cell.
  So, pieces in the same cell don't attack each other.

figure.diagram-container
  .diagram
    | fen:1r1kr3/3nbbQ1/6p1/4p3/1qp1p3/PR1P1NPP/4nP2/2B1KR1B:
  figcaption.
    The white king under check cannot take the knight,
    and Rxb4 is not possible.

p.
  Pawns are Berolina pawns: they move one square diagonally forward and
  capture one square orthogonally forward.

h3 Source

p
  | This variant is mentioned in 
  a(href="https://www.jsbeasley.co.uk/encyc.htm")
    | The Classified Encyclopedia of Chess Variants
  | .