The countsquares filter takes a range and a set filter as its arguments:
countsquares range set-filter

The filter returns true if the number of the squares in the set denoted by its set filter argument lies within its range.

For example,

	countsquares 2 4 P
is true when the current position has between 2 and 4 white pawns.

The countsquares filter is countable and counts the number of squares in its associated set. Therefore, it may be sorted. For example,

	sort countsquares 1 64 attack (Q _)
will sort games by the maximum number of empty squares attacked by a white Queen. This is because
	attack (Q _)
represents the set of empty squares attacked by a white Queen in the current position.