xy-pair nodes are used in conjunction with a fuzzy curve node to dynamically define transition points on a fuzzy curve.
The two child-nodes define the x and y coordinates of the point on the fuzzy curve. The leftmost child-node defines the x position while the rightmost child-node defines the y position (the trueness level for the given x value).
Child-nodes of the xy-pair can be of any type, but be aware that the node defining the y (trueness) coordinate should be something that is constrained to values from false (-1) to true (+1) when used in a dependency network.
See fuzzy curve.