plyfilter is a numeric filter whose value is the ply value of the current position. The ply value of the initial position is
0, and the ply value of any other position is one greater than the ply value of its parent.
plyfilter is used in
averagedistance.cqlwhere the filter
requires that the ply of the current position be greater than 10. The
ply filter is also used there
to compute the average move length: