The ▦ character

The ▦ (ascii: .) filter is a set filter that represents the 64 squares of the chessboard. It matches any position. The ▦ filter is equivalent to

      a-h1-8

For example, to check if the white queen attacks 27 squares, use

      ▦←♕==27

Technically, this only works if there is at most one white on the board. To check that any white queen attacks 27 squares, use

      z∊♕ ▦←z==27