Reading through the math node docs, I came across a math function named "ping-pong".

The docs state that ping-pong does the following

The output value is moved between 0.0 and the Scale based on the input value.

What in the world does that mean? Can anyone tell me what the actual ping-pong function is? What input values lead to an output of 0, and what input values lead to an output of "scale"?