findPlaneCrossing 0 0 50 0 0 1;

// In this example, findPlaneCrossing selects all keys

// found on the toe markers LTOE and RTOE that penetrate the

// "floor" of the scene, here defined as being all points for

// which the Z component is 50 millimeters. The directional

// arguments 0 0 1 define the vector of the normal for the 

// plane, in this case the normal of the plane is aligned with

// world Z, pointing straight "up". If you switch the Z 

// component of the direction argument from 1 to -1, the 

// command will find all keys that are above the floor. 

// This example assumes a Z-up environment.