ply

The ply filter 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.

Examples

The ply filter is used in averagedistance.cql where the filter
  ply>10

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:

  Sum/ply>4*Scale