connectedpawns

The connectedpawns filter has a value equal to the set of connected pawns in the position:
  connectedpawns

For example, the value of the connectedpawns filter in the position that is the start position of a chess game has value the 16 squares a-h2 and a-h7.

The connectedpawns filter is equivalent to:

  flipcolor{
    P&
     horizontal 1
        vertical 0 7 P}